How many gallons of blue must be used

Question

A certain paint is to be mixed with 3 parts yellow 2 parts blue. Twelve gallons of paint are needed.

How many gallons of blue must be used?

Answer 1

3 parts yellow + 2 parts blue = 5 parts in total.

This means that 3/5 of the total paint must be yellow, and 2/5 of the paint must be blue.

3/5 of 12 gallons is (3/5) * 12 = 36/5 = 7.2

2/5 of 12 gallons is (2/5) * 12 = 24/5 = 4.8

So 7.2 gallons of yellow and 4.8 gallons of blue.