5 prefects are to be chosen from 6 boys and 4 girls.in how many ways can this be done if
a)all the prefects are boys
b)there are at least two girls
How many ways can 5 boys be chosen from 6?.a)all the prefects are boys
At least two means 2 up to 4 girls are to be chosen. Add the 3 cases up.b)there are at least two girls
2 girls and 3 boys, 3 girls and 2 boys, 4 girls and 1 boy.
$\displaystyle \binom{4}{2}\binom{6}{3}+\binom{4}{3}\binom{6}{2}+ \binom{4}{4}\binom{6}{1}$