4 girls and 8 boys are standing together. In how many ways can a 7- person committee be selected from the group if at least 2 girls must be included?
NOTE: This answer is WRONG.
So it is an example of what will not work!
Take 2 girls first 4C2
then take 5 from what is left 10C5
then multiply the answers together.
That is assuming all committee members are equal.
when you choose 2 girls then 5 other members you overcount (you can choose all 4 girls by choosing the first two, then choosing the other 2 girls and other 3 boys when you choose the other five, OR by choosing the last two girls first, then choosing the first two girls +other 3 boys)