math
posted by amy on .
Assume that there are 6 unfilled roles: 1 male and 5 female. There are 5 men and 7 women, including Ann, auditioning for a part in the play.
How many of these casts include Ann?

If Ann is in, then we need 1 male from the 5 men, and 4 more females from the remaining 6 women
Number of casts = 1 x C(5,1) x C(6,4) = 75
or
number of ways with no restriction = C(5,1) x C(7,5) = 105
number of ways without Ann = C(5,1) x C(6,5) = 30
So number of ways with Ann = 10530 = 75