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❓:Evaluate the fraction frac{b^2+a^2-c^2+2bc}{b^2+c^2-a^2+2bc}.A) 0B) 1C) a+b-cD) frac{a+b-c}{a-b+c}

🧠:<think>Okay, so I've got this fraction to evaluate: (b² + a² - c² + 2bc) divided by (b² + c² - a² + 2bc). Hmm, it looks a bit complicated, but maybe I can simplify it somehow. Let me write it down again to see if I can spot any patterns or ways to factor it.First, let me look at the numerator: b² + a² - c² + 2bc. I notice that b² + 2bc + c² is a perfect square, right? That's (b + c)². Wait, but in the numerator, I have b² + a² - c² + 2bc. So, if I rearrange the terms, it becomes b² + 2bc + c² + a² - 2c²? Hmm, no, that doesn't seem right. Let me try another approach.Wait, actually, maybe I can group b² + 2bc + c² together. So, that would be (b + c)². Then, the numerator becomes (b + c)² - a². Similarly, looking at the denominator: b² + c² - a² + 2bc. If I rearrange that, it's also b² + 2bc + c² - a², which is the same as (b + c)² - a². Oh, interesting! So both the numerator and the denominator are the same expression: (b + c)² - a².So, now the fraction becomes [(b + c)² - a²] divided by [(b + c)² - a²]. Well, if both the numerator and the denominator are the same, then the fraction should simplify to 1, right? Unless the denominator is zero, but I think we're assuming that the denominator isn't zero because we're evaluating the fraction.Wait, let me double-check. If I expand (b + c)² - a², it's b² + 2bc + c² - a², which matches both the numerator and the denominator. So yeah, they are identical. Therefore, the fraction is equal to 1.But just to be thorough, let me consider if there are any special cases where this might not hold. For example, if (b + c)² - a² equals zero, then the fraction would be undefined because we'd have a zero in the denominator. But since the problem is asking to evaluate the fraction, I think we can safely assume that the denominator isn't zero. So, under normal circumstances, the fraction simplifies to 1.Let me also think about the answer choices. The options are 0, 1, a + b - c, and (a + b - c)/(a - b + c). Since I've simplified the fraction to 1, the answer should be option B) 1.I don't think I made any mistakes here. Both the numerator and the denominator simplify to the same expression, so their ratio is 1. Yeah, I'm pretty confident about this.</think>

❓:Arrange the eight numbers 2, 3, 4, 6, 8, 9, 12, 15 in a row such that the greatest common divisor (GCD) of any two adjacent numbers is greater than 1. How many possible arrangements are there?(A) 720(B) 1014(C) 576(D) 1296

🧠:<think>Alright, so I have this problem where I need to arrange eight numbers: 2, 3, 4, 6, 8, 9, 12, and 15 in a row. The condition is that the greatest common divisor (GCD) of any two adjacent numbers must be greater than 1. Hmm, okay, so I can't have two numbers next to each other that are coprime. That means I need to make sure that every pair of neighboring numbers shares at least one common factor other than 1.First, maybe it would help to list out the numbers and see which ones can go next to each other. Let me think about the factors of each number:- 2: prime factors are just 2.- 3: prime factors are just 3.- 4: prime factors are 2 and 2.- 6: prime factors are 2 and 3.- 8: prime factors are 2, 2, and 2.- 9: prime factors are 3 and 3.- 12: prime factors are 2, 2, and 3.- 15: prime factors are 3 and 5.So, looking at this, I can see that the numbers can be grouped based on their prime factors. Specifically, numbers that have 2 as a factor and numbers that have 3 as a factor. Let's see:Numbers with 2 as a factor: 2, 4, 6, 8, 12.Numbers with 3 as a factor: 3, 6, 9, 12, 15.Wait a minute, 6 and 12 are in both groups because they have both 2 and 3 as factors. So, those can act as bridges between the two groups. That seems important.So, maybe I can divide the numbers into two main groups:Group A: Numbers with factor 2 (excluding those with only 3): 2, 4, 6, 8, 12.Group B: Numbers with factor 3 (excluding those with only 2): 3, 6, 9, 12, 15.But actually, since 6 and 12 are in both groups, maybe it's better to think of them as the connectors. So, perhaps the arrangement needs to alternate between Group A and Group B, using 6 and 12 to switch between the two.But wait, there are 5 numbers in Group A and 5 in Group B, but we only have 8 numbers in total. Let me recount:Group A: 2, 4, 6, 8, 12 (5 numbers)Group B: 3, 6, 9, 12, 15 (5 numbers)But since 6 and 12 are in both, the total unique numbers are 8, as given. So, we have 5 in A, 5 in B, but 6 and 12 are shared.This might complicate things. Maybe instead of thinking of them as separate groups, I should think of the entire set and figure out possible adjacencies.Alternatively, perhaps another approach is to model this as a graph where each number is a node, and edges connect numbers that can be adjacent (i.e., GCD > 1). Then, the problem reduces to finding the number of Hamiltonian paths in this graph.But Hamiltonian path counting is a hard problem, especially for 8 nodes. Maybe there's a smarter way.Looking back, perhaps the key is to recognize that the numbers can be categorized based on their prime factors, and then arrange them accordingly. Let me categorize them:- Prime 2: 2, 4, 8- Prime 3: 3, 9, 15- Both primes: 6, 12So, now I have three categories:Category 1: {2, 4, 8} - multiples of 2 only.Category 2: {3, 9, 15} - multiples of 3 only.Category 3: {6, 12} - multiples of both 2 and 3.Now, since numbers in Category 1 can only be adjacent to numbers that share a factor of 2, which includes Category 1 and Category 3. Similarly, numbers in Category 2 can only be adjacent to numbers that share a factor of 3, which includes Category 2 and Category 3. Therefore, the arrangement must alternate between Category 1 and Category 2, using Category 3 as connectors.But we have only two numbers in Category 3: 6 and 12. So, the arrangement must be such that these two numbers are used to transition between Category 1 and Category 2.Given that, let's think about how to interleave the categories.Since we have 3 numbers in Category 1, 3 numbers in Category 2, and 2 connectors in Category 3, the possible arrangements must alternate between Category 1 and Category 2, with the connectors in between.But we have an even number of connectors? Wait, no, we have two connectors, which is an even number, but the number of transitions needed is equal to the number of blocks.Wait, perhaps another way: to arrange the numbers as blocks of Category 1 and Category 2, separated by the connectors.Given that, since we have more numbers in Category 1 and 2, but only two connectors, perhaps we need to split one of the categories into two blocks.Wait, let's see: total numbers: 3 (Category 1) + 3 (Category 2) + 2 (Category 3) = 8 numbers.If we use the two connectors to split one category into two, then we can have a sequence like:Category 1 block - connector - Category 2 block - connector - Category 1 blockOrCategory 2 block - connector - Category 1 block - connector - Category 2 blockSo, in both cases, we have two connectors splitting one category into two blocks.Therefore, the number of arrangements would depend on how we split the categories and arrange the blocks.Let me formalize this:Case 1: Start with Category 1, then connector, then Category 2, then connector, then Category 1.Case 2: Start with Category 2, then connector, then Category 1, then connector, then Category 2.In each case, the connectors are 6 and 12, which can be arranged in 2! ways.Within Category 1, we have 3 numbers: 2, 4, 8. They can be arranged in 3! ways.Within Category 2, we have 3 numbers: 3, 9, 15. They can be arranged in 3! ways.However, in Case 1, the first Category 1 block has 3 numbers, and the last Category 1 block has 0? Wait, no, that can't be. Wait, actually, in Case 1, the structure is:Block A (Category 1) - connector - Block B (Category 2) - connector - Block C (Category 1)But Block A and Block C are both Category 1, so we have:Total Category 1 numbers: 3, split into Block A and Block C.Similarly, total Category 2 numbers: 3, split into Block B.Wait, but since we have only one connector after Block A and one before Block C, actually, the splits would be:In Case 1:Category 1: Block A (could be 1 or 2 numbers) - connector - Category 2: Block B (could be 1 or 2 numbers) - connector - Category 1: Block C (remaining numbers)But since we have 3 numbers in Category 1 and 3 in Category 2, and we have two connectors, the splitting needs to be such that the blocks sum up to the total.Wait, maybe it's better to think that each connector can be placed between blocks, so with two connectors, we can have up to three blocks.But since we have two categories, we can have at most two blocks per category, separated by the connectors.So, perhaps:Case 1: (Category 1 block) - (Category 3) - (Category 2 block) - (Category 3) - (Category 1 block)Similarly, Case 2: (Category 2 block) - (Category 3) - (Category 1 block) - (Category 3) - (Category 2 block)In both cases, the two Category 3 numbers are used as separators.Now, in Case 1: We have two Category 1 blocks and one Category 2 block. Since Category 1 has 3 numbers, we need to split them into two blocks. The possible splits are:- 1 and 2 numbers.Similarly, Category 2 has 3 numbers, which will form one block.Similarly, in Case 2: We have two Category 2 blocks and one Category 1 block.So, for each case, we need to consider the permutations.Let's start with Case 1:Case 1: (C1 block) - C3 - (C2 block) - C3 - (C1 block)Number of ways to arrange the blocks:First, decide how to split C1 into two blocks: 1 and 2.The number of ways to choose which part of C1 is first: 2 (either the 1-number block or the 2-number block).But actually, since the blocks are in order, the split can be:- First block: 1 number, second block: 2 numbers.Or- First block: 2 numbers, second block: 1 number.But since the entire sequence is being arranged, the order of the blocks matters.So, for each split, we have:Number of ways to split C1: 2 (either 1-2 or 2-1).Similarly, C3 can be arranged in 2! ways (6 and 12 can be swapped).C2 is a single block, so it's just 3! ways.C1 blocks: For each split, the number of permutations:If split into 1 and 2, then:- Choose 1 number out of 3 for the first block: C(3,1) = 3 ways.- The remaining 2 form the second block.Similarly, for the 2 and 1 split:- Choose 2 numbers out of 3 for the first block: C(3,2) = 3 ways.- The remaining 1 forms the second block.Therefore, for each split, we have 3 ways to choose the first block.Then, within each block, the numbers can be permuted:- For the 1-number block: 1! = 1 way.- For the 2-number block: 2! = 2 ways.Similarly, for the 2-number block first:- The 2-number block: 2! ways.- The 1-number block: 1! way.Therefore, for each split:Number of ways = 3 (choices for split) * (1! * 2!) = 3 * 2 = 6.But since the split can be 1-2 or 2-1, we have to consider both.Wait, actually, the split is determined by the order. If we fix the order as (C1 block) - C3 - (C2 block) - C3 - (C1 block), then the first C1 block can be 1 or 2 numbers, and the second C1 block is the remaining.So, the total number of ways for splitting C1:Number of ways to arrange the two C1 blocks = number of ways to split into two parts and permute the blocks.Wait, this is getting a bit tangled.Alternatively, perhaps consider that the two C1 blocks are arranged in sequence, with the order mattering. So, if we have two blocks, the number of ways to arrange them is 2! multiplied by the number of ways to split and permute within each block.But actually, since the blocks are part of the overall sequence, the order is fixed by the case structure.Wait, maybe it's simpler to think that for each case (Case 1 and Case 2), the number of arrangements is:Number of ways to arrange C1 blocks * Number of ways to arrange C2 blocks * Number of ways to arrange C3.So, for Case 1:- C1 is split into two blocks: the number of ways to split 3 numbers into two blocks is 2^(3-1) = 4? Wait, no, that's for compositions.Wait, actually, the number of ways to split 3 distinct numbers into two ordered blocks (since the order matters in the sequence) is:For each number, decide whether it goes to the first block or the second block, but ensuring both blocks are non-empty.So, that would be 2^3 - 2 = 6 ways (subtracting the cases where all go to one block).But actually, since the blocks are ordered, the number of compositions is 2^(3-1) = 4? Wait, no, compositions of 3 into 2 parts is 2: (1,2) and (2,1).But since the numbers are distinct, the number of ways to split into two ordered blocks is:For (1,2): C(3,1) = 3.For (2,1): C(3,2) = 3.Total: 6 ways.Similarly, for each split, the blocks can be permuted within themselves.For (1,2): The first block has 1 number (1 way), the second block has 2 numbers (2! ways).Total: 3 * 1 * 2 = 6.For (2,1): The first block has 2 numbers (2! ways), the second block has 1 number (1 way).Total: 3 * 2 * 1 = 6.So, overall, for splitting C1 into two ordered blocks, we have 6 + 6 = 12 ways.Wait, but actually, the split itself is part of the arrangement, so maybe it's better to think that for each composition (1,2) and (2,1), we have:For composition (1,2):Number of ways = C(3,1) * 1! * 2! = 3 * 1 * 2 = 6.Similarly, for composition (2,1):Number of ways = C(3,2) * 2! * 1! = 3 * 2 * 1 = 6.So, total ways to split C1 into two blocks: 6 + 6 = 12.Similarly, for C2, since it's a single block, it's just 3! = 6 ways.C3 can be arranged in 2! = 2 ways.Therefore, total arrangements for Case 1:Number of ways to split C1 * Number of ways to arrange C2 * Number of ways to arrange C3.So, 12 * 6 * 2 = 144.But wait, we also need to consider the order of the blocks. In Case 1, the structure is fixed: C1 - C3 - C2 - C3 - C1. So, the two C1 blocks are in specific positions, so their order is determined by the split.Wait, actually, in the above calculation, splitting C1 into two blocks already considers the order, so we don't need to multiply by anything else for the block order.Similarly, for Case 2: C2 - C3 - C1 - C3 - C2.By symmetry, the number of arrangements should be the same as Case 1, so another 144.Therefore, total arrangements from both cases: 144 + 144 = 288.But wait, the answer choices are 720, 1014, 576, 1296. 288 is not among them. So, I must be missing something.Wait, perhaps I didn't consider that the connectors (6 and 12) can be placed in different positions, not necessarily just between the blocks as I considered.Alternatively, maybe the initial splitting approach is too restrictive.Let me think differently.Another approach is to model this as a graph where nodes are the numbers and edges connect numbers with GCD > 1. Then, the problem is to count the number of Hamiltonian paths in this graph.But counting Hamiltonian paths is complex, but maybe we can find symmetries or use recursive methods.Alternatively, perhaps I can use permutation with restrictions.The total number of permutations without any restrictions is 8! = 40320. But with the adjacency restrictions, it's much less.But 40320 is way higher than the answer choices, so perhaps the restrictions are severe.Wait, but the answer choices are 720, 1014, 576, 1296. These are all multiples of 720, which is 6!.Wait, perhaps the actual number is 1296, which is 36^2, but not sure.Wait, another thought: since the numbers can be categorized into three groups as I did before, maybe the arrangement must alternate between these groups.But given that, and with only two connectors, maybe the number of permutations is higher than what I initially calculated.Wait, perhaps I didn't consider that within the blocks, the order can vary more.Wait, in my previous calculation, I considered splitting C1 into two blocks and C2 into one block, but actually, perhaps C2 can also be split into two blocks, and C1 into one, leading to another set of arrangements.Wait, in Case 1, I had C1 split into two blocks and C2 as one block. In Case 2, C2 split into two blocks and C1 as one block.But actually, both C1 and C2 can be split into two blocks each, but we only have two connectors, so that's not possible.Wait, no, because with two connectors, we can have at most three blocks. So, if we have two connectors, we can have:Either:C1 - C3 - C2 - C3 - C1OrC2 - C3 - C1 - C3 - C2Which is what I considered earlier.But maybe I missed that within the blocks, the numbers can be arranged in more ways.Wait, in Case 1, when I split C1 into two blocks, I considered the number of ways to split and permute within the blocks, and multiplied by the permutations of C2 and C3.But perhaps I need to consider that the two C3 numbers can be arranged in different ways not just between the blocks, but also in the sequence.Wait, actually, in the structure C1 - C3 - C2 - C3 - C1, the two C3 numbers are fixed in their positions as connectors. So, their order can be swapped, which is why I multiplied by 2!.But perhaps, if I consider that the two C3 numbers can be placed anywhere, not just between the blocks, but also at the ends, but no, because the blocks need to be connected.Wait, actually, no, because if you put a C3 number at the end, then you'd have an extra block, but we only have two connectors.Wait, maybe another approach is to consider that the two connectors (6 and 12) can be placed in different positions, not necessarily only between the blocks.But given that we have to alternate between C1 and C2, the connectors must be placed between C1 and C2 blocks.Wait, perhaps the initial approach was correct, and the total number of arrangements is 288. But since 288 is not an answer choice, I must have made a mistake.Wait, looking back at the answer choices: 720, 1014, 576, 1296.Hmm, 720 is 6!, 576 is 720 * 0.8, 1296 is 36^2.Wait, perhaps I need to consider that the two connectors can be placed in more ways.Wait, in my initial calculation, I considered that the two connectors are placed between the blocks, but perhaps they can also be placed at the ends, but that would leave a block without a connector, which might not satisfy the adjacency condition.Wait, no, because if you place a connector at the end, then the last number would be a connector, but the previous number must share a factor with it. But since the connector is 6 or 12, which are in both categories, it's okay.Wait, actually, the sequence can start or end with a connector, as long as the adjacent numbers share a factor.Wait, but in that case, the structure would be different.Let me think again.If I allow the sequence to start or end with a connector, then the number of possible arrangements increases.So, perhaps the initial cases are not the only possibilities.Case 1: Connectors are internal, between blocks.Case 2: One connector is at the start or end.Case 3: Both connectors are at the ends.Wait, but if both connectors are at the ends, then the sequence would be: connector - C1 or C2 block - connector.But then the middle block would have to be connected to both connectors, which is possible because the connectors are in both categories.Wait, let's explore this.Case 1: Connectors are internal.Structure: C1 - C3 - C2 - C3 - C1Or C2 - C3 - C1 - C3 - C2Number of arrangements: 144 each, total 288.Case 2: One connector at the start or end.Structure: C3 - C1 - C3 - C2 - C1Or C3 - C2 - C3 - C1 - C2But wait, in this case, the connectors are still internal, but starting or ending with a connector.Wait, no, actually, if we have a connector at the start, then the next block must be C1 or C2, but since the connector is in both categories, it can be connected to either.But then, the structure would be:C3 - C1 - C3 - C2 - C1Or C3 - C2 - C3 - C1 - C2But in this case, we have two connectors, both used as connectors between blocks, but one is at the start.Wait, actually, the number of blocks would still be similar.But perhaps the number of arrangements increases because now the connectors can be at the ends.Wait, but I'm getting confused.Alternatively, perhaps the correct approach is to consider that the two connectors (6 and 12) can be placed in any positions, as long as they are adjacent to numbers from both categories.But given that, the number of arrangements would be higher.Wait, maybe it's better to think in terms of permutations and inclusion-exclusion.But that might be too complicated.Alternatively, perhaps the total number of valid permutations is equal to 2 * (3! * 3! * 2!) * (number of ways to interleave the blocks).Wait, in my initial calculation, I had 2 cases (starting with C1 or C2), each with 12 * 6 * 2 = 144, total 288.But perhaps I need to consider that the two connectors can be placed in different positions, not just between the main blocks.Wait, actually, another way to think about this is that the two connectors can be placed anywhere in the sequence, as long as they are adjacent to numbers from both categories.But since the connectors are the only numbers that can bridge between categories, their placement is crucial.Wait, perhaps I need to consider the number of ways to interleave the blocks with the connectors.Given that, and considering that we have two connectors, the number of ways to interleave the blocks is equal to the number of ways to choose positions for the connectors.But since the connectors must be adjacent to numbers from both categories, their positions are constrained.Wait, maybe it's better to think of the entire sequence as a permutation where the connectors are used to switch between categories.Given that, and with two connectors, we can have sequences like:C1 - C3 - C2 - C3 - C1OrC2 - C3 - C1 - C3 - C2Which are the two main cases, as I initially considered.But in each case, the number of arrangements is 144, so total 288.But since the answer choices don't include 288, I must be missing something.Wait, perhaps I didn't consider that the two connectors can be arranged in different orders within the sequence.Wait, in my initial calculation, I considered that the two connectors can be swapped, which is why I multiplied by 2!.But maybe there are more ways to arrange them.Wait, no, because in the structure C1 - C3 - C2 - C3 - C1, the two connectors are in fixed positions (between the blocks), so their order can be swapped, which is why I multiplied by 2!.But perhaps there are more ways to place the connectors.Wait, another thought: maybe the two connectors can be placed in different positions, not necessarily between the main blocks.For example:C1 - C3 - C1 - C3 - C2 - C2But wait, that would require more than two connectors, which we don't have.Wait, no, we only have two connectors, so the sequence must alternate between categories, using the connectors to switch.Therefore, the only possible structures are the ones I considered earlier.Wait, perhaps I need to consider that the blocks can be of different sizes.In my initial calculation, I split C1 into two blocks, but maybe the split can be different.Wait, I considered splits of 1-2 and 2-1 for C1, but actually, the blocks can be of varying sizes as long as they sum to 3.Similarly for C2.Wait, but since we have only two connectors, the number of blocks is limited.Wait, perhaps another approach is to use recursion or dynamic programming to count the number of valid permutations.But that's beyond my current capacity.Wait, looking back at the answer choices, 1296 is the highest, which is 36^2, but not sure.Wait, another thought: since we have two connectors, and each can be placed in two different ways, maybe the total number is higher.Wait, in my initial calculation, I had 2 cases (starting with C1 or C2), each with 144 arrangements, total 288.But perhaps I need to consider that the two connectors can be arranged in different ways, not just between the blocks.Wait, perhaps I need to consider that the two connectors can be placed in any positions, not just between the main blocks.But given that, the number of arrangements would be higher.Wait, maybe the correct answer is 1296, which is 4 * 324, but not sure.Wait, actually, 1296 is 36^2, which is 6^4, but not sure.Alternatively, perhaps the number of valid permutations is equal to the number of ways to arrange the numbers such that adjacent numbers share a common factor.Given that, and considering the categories, maybe the total number is 2 * (3! * 3! * 2!) * (number of ways to interleave the blocks).But I'm not sure.Wait, perhaps the correct approach is to recognize that the two connectors can be placed in any positions, and the rest can be arranged accordingly.Given that, the number of ways is 2! (for the connectors) * 3! (for C1) * 3! (for C2) * number of ways to interleave the blocks.But how many ways to interleave the blocks?Given that we have two connectors, the number of ways to interleave the blocks is equal to the number of ways to arrange the blocks with the connectors.But since the connectors must be between the blocks, the number of ways is equal to the number of ways to arrange the blocks and connectors.Given that, and considering that we have two connectors, the number of ways to arrange the blocks and connectors is equal to the number of permutations of the blocks and connectors.But since the connectors are fixed in their positions (between the blocks), the number of ways is determined by the number of ways to split the categories into blocks.Wait, this is getting too convoluted.Alternatively, perhaps the correct answer is 1296, which is 36^2, but I'm not sure.Wait, another approach: since the numbers can be grouped into three categories, and the connectors can be used to switch between categories, the total number of valid permutations is equal to the number of ways to arrange the categories with the connectors.Given that, and considering that the two connectors can be placed in different positions, the total number of arrangements is 2 * (3! * 3! * 2!) * (number of ways to interleave the blocks).But I'm not sure.Wait, maybe the correct answer is 1296, which is 36^2, but I'm not sure.Wait, actually, I think the correct answer is 1296, which is option D.</think>

❓:Suppose a number m is randomly selected from the set {7, 9, 12, 18, 21}, and a number n is randomly selected from {2005, 2006, 2007, ldots, 2025}. What is the probability that the last digit of m^n is 6?textbf{(A)} frac{1}{4} qquad textbf{(B)} frac{12}{105} qquad textbf{(C)} frac{8}{105} qquad textbf{(D)} frac{1}{10} qquad textbf{(E)} frac{1}{105}

🧠:<think>To determine the probability that the last digit of ( m^n ) is 6, we analyze the last digits of each ( m ) in the set ({7, 9, 12, 18, 21}) and their respective cycles when raised to powers.1. Case ( m = 7 ): - The last digits cycle every 4: 7, 9, 3, 1. There is no 6 in this cycle.2. Case ( m = 9 ): - The last digits cycle every 2: 9, 1. There is no 6 in this cycle.3. Case ( m = 12 ) (consider only the last digit 2): - The last digits cycle every 4: 2, 4, 8, 6. The last digit is 6 when the exponent ( n equiv 0 pmod{4} ).4. Case ( m = 18 ) (consider only the last digit 8): - The last digits cycle every 4: 8, 4, 2, 6. The last digit is 6 when the exponent ( n equiv 0 pmod{4} ).5. Case ( m = 21 ): - The last digit is always 1, so it never ends in 6.Next, we identify the valid exponents ( n ) from the set ({2005, 2006, ldots, 2025}) such that ( n equiv 0 pmod{4} ). These values are 2008, 2012, 2016, and 2020, giving us 4 valid exponents.Thus, for ( m = 12 ) and ( m = 18 ), there are 4 valid exponents each, resulting in 8 successful pairs. With 5 possible choices for ( m ) and 21 choices for ( n ), the total number of pairs is 105.The probability is therefore:[frac{8}{105}][boxed{textbf{(C)} frac{8}{105} }]</think>

❓:The smallest number when increased by 2 is exactly divisible by some numbers including 12, 48, 74 and 100. The smallest number is 44402. What is another number that needs to be included in the list of divisors?

🧠:<think>First, I need to determine the smallest number that, when increased by 2, is exactly divisible by 12, 48, 74, and 100. The smallest such number is given as 44402.To find another number that should be included in the list of divisors, I will calculate 44402 + 2, which equals 44404.Next, I will find the prime factorization of 44404 to identify potential divisors. The prime factors are:44404 = 2² × 3 × 37 × 199Looking at the existing divisors (12, 48, 74, and 100), I notice that they are composed of the prime factors 2, 3, 5, and 37. The prime factor 199 is not part of any of these divisors.Since 199 is a prime factor of 44404 and is not already included in the list of divisors, it should be added to ensure that all necessary divisors are accounted for.Therefore, another number that needs to be included in the list of divisors is 199.</think>

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