Ahardware store sells single digits to be used for house numbers. there are five 5s, four 4s, three 3s and two 2s available. from this selection of digits, a customer is able to purchase her three-digit house number. how many possible three-digit house numbers could this customer make?

Since there are no restrictions on the three-digit numbers (for example no repetitions), we actually don't care about the values of the digits. All we need to know is that there are

possible digits, and that we have to extract a triplet from here.

For problems like this we have the binomial coefficient, defined as

This number tells you how many subsets of k elements you can extract from a set of n elements. So, in your case, you want to compute

there will be 35 boys in each team. : )