44. Boys and girls sit on chairs numbered from the first to the ninth, with 5 boys and 4 girls sitting down. Boys sit on chairs with odd numbers, and girls sit on chairs with even numbers. In how many ways can this be done?
Official solution
44. Boys can sit on chairs with odd numbers in 5!=120 ways, and girls on chairs with even numbers in −4!=24 ways. In total, we get 120⋅24=2880 ways.
Source: NuminaMath-1.5,
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