Magentarita,

There is no way to be sure you will get a complete set, no matter how many packages you buy. For example, you might buy a million packages and they might all turn out to have the same player-- not likely, but possible.

I think the problem is asking you to find how many packages you have to buy, on average, to get a complete set. More formally, let's say X is the number of packages required to get a complete set. X is a random variable, and you would like to find (or estimate) its expected value.