at least one woman means one or more. thus, you want the sum of the number of committees of each type below.

1 woman, 4 men

2 women, 3 men

3 women, 2 men

4 women, 1 man

5 women

note, this is not a probability problem. it is a combinatorics problem. in general, there is no need to find the total possible outcomes. unless you want to do the compliment perhaps. we can get the same answer by finding the numer of committees that have no women, and subtract them from the total number of possible committees. can you finish?