The ratio given says this - 3 puppies : 2 adults = 5 total dogs
You are given (?) puppies : (?) adults = 80 total dogs
In this case, you are trying to find the number of puppies, so you do not need to care about the number of adults. You need to compare the ratio with the actual amount.
Total/puppies = total/puppies
5/3 = 80/(?)
Now, cross multiply.
5(?) = 240
Divide both sides by 5 and you get your answer.
(?) = 48
