Maths Olympiad Prep

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Combinatorics Difficulty 3.0 Junior Find the answer

To arrange a performance program with 6 singing programs and 4 dance programs, where no two dance programs can be adjacent, how many different arrangements are possible? (Only the formula needs to be written, no need to calculate.)

A number or a short expression. Spacing and $ signs are ignored.

Solution

This problem can be solved using the method of inserting spaces. Since no two dance programs can be adjacent, we can consider the space before and after each of the 6 singing programs as a potential position for inserting a dance program, resulting in 7 spaces. We need to arrange the dance programs into these spaces to ensure they are not adjacent. There are P74P_{7}^{4} ways to do this. After arranging the dance programs, there are A66A_{6}^{6} ways to arrange the singing programs.

Therefore, the total number of arrangements is P74×A66P_{7}^{4} \times A_{6}^{6}.

The answer is P74×A66\boxed{P_{7}^{4} \times A_{6}^{6}}.

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Source: NuminaMath-1.5, licensed Apache-2.0. Statement and solution reproduced as published; topic and difficulty added by this site.