1.

Find the number of ways in which 4 boys and 5 girls can be arranged in a row so that no two boys are together and no two girls are together.

Answer»

No two boys and no two girls are together means the boys & girls must sit alternately. 

Four boys can be permuted in 4! ways & the 5 girls in 5! ways. 

∴ The total number of ways is 5! × 4! ways.



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