• June 3rd 2010, 03:29 PM
cantcount
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
• June 3rd 2010, 04:10 PM
galactus
Quote:

Originally Posted by cantcount
5 prefects are to be chosen from 6 boys and 4 girls.in how many ways can this be done if

Quote:

a)all the prefects are boys
How many ways can 5 boys be chosen from 6?.

Quote:

b)there are at least two girls
At least two means 2 up to 4 girls are to be chosen. Add the 3 cases up.

2 girls and 3 boys, 3 girls and 2 boys, 4 girls and 1 boy.

$\binom{4}{2}\binom{6}{3}+\binom{4}{3}\binom{6}{2}+ \binom{4}{4}\binom{6}{1}$