There are balloons for sale at the fair, 7/10 of the balloons are blue, 1/5 are red, and the rest are yellow balloons. How many balloons are there in all?

Answer 1

well, you know that 9/10 are either blue or red.

So, 1/10 are yellow. If you can ascertain how many yellow balloons there are, then you can figure out the total.