Find the number of ways in which 5 boys and 4 girls can be arranged on a circular table such that no two girls sit together and 2 particular boys are always together?
Question
Find the number of ways in which 5 boys and 4 girls can be arranged on a circular table such that no two girls sit together and 2 particular boys are always together?
Solution 1
To solve this problem, we need to use the principles of permutations and combinations. Here are the steps:
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Since it's a circular arrangement, we fix one position. Let's consider the two particular boys as a single entity since they always have to be together. So now we have 4 entities (3 boys and 1 entity of 2 boys) and 4 girls to arrange.
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The boys can be arranged around the table in (4-1)!=3! ways (since in circular permutations, we subtract one from the total number of items).
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The two boys considered as a single entity can arrange themselves in 2! ways.
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Now, we have to arrange the girls. Since no two girls can sit together, we can think of arranging the girls in the spaces between the boys. There are 4 spaces between the boys (including the space before the first boy and after the last boy). The girls can be arranged in these spaces in 4P4 ways.
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Therefore, the total number of arrangements is (3! * 2! * 4P4) = (6 * 2 * 24) = 288 ways.
Solution 2
Sure, here is the step by step solution:
Step 1: Since it is a circular arrangement, we fix one person first. Let's fix one of the boys. Now we have 4 boys and 4 girls left.
Step 2: Two particular boys are always together. We can consider these two boys as one entity. So, now we have 3 boys and 1 entity (2 boys) and 4 girls.
Step 3: As no two girls can sit together, we have to place the girls in between the boys. We have 4 places (between the boys) and 4 girls. The number of ways to arrange the 4 girls in 4 places is 4!.
Step 4: Now, we have 4 entities (3 boys and 1 entity of 2 boys) left. The number of ways to arrange these 4 entities in a circle is (4-1)! = 3!.
Step 5: But the 2 boys (who are considered as one entity) can be arranged among themselves in 2! ways.
Step 6: Therefore, the total number of ways is 4! * 3! * 2! = 576 ways.
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