+2653 In how many ways can we distribute 13 pieces of identical candy to 5 kids, if the two youngest kids are twins and insist on receiving at least four pieces each?
+135 To account for the conditional at the beginning, let's just give the two youngest kids four candies off the bat. That leaves you with 5 candies to divide between 5 kids, which is a simple stars and bars problem (if you don't know what it is, look it up it's really cool :) )
This means the answer is 9 choose 4 which is (9!)/(4!)*(5!) = (9 * 8 * 7 * 6) / 24 = 9 * 7 * 2 = 112 ways
