Answer:
Together the football and baseball cards make up 77/100 of Heath's card collection.
Explanation:
First, you compute the fractions (sorry, I can't think of the right word) so that they have the same denominator. 7/100 = 7/100, and 7/10 = 70/100. Now you're able to add them. 7/100 + 70/100 = 77/100. This fraction is already in simplest form, so there's no need to simplify. Therefore, together the football and baseball cards make up 77/100 of Heath's card collection.