Winter is almost here and most animals are migrating to warmer countries. There are 15 bird families living near the mountain. If 28 bird families flew away to africa and 13 bird families flew away to asia How many bird families flew away for the winter?
There are 15 bird families living near the mountain. 
28 bird families flew away to Africa. 
13 bird families flew away to Asia. 

So, we can say that a total of 28 + 13 = 41 bird families flew away for the winter.