Question 2
A painter has five ten-gallon cans of paint: red, green, blue, yellow and orange, one colour per can. The amount of paint left in each can is a whole number of gallons. 1) Red and green total 8 gallons. 2) Blue and yellow total 10 gallons. 3) Green, yellow and orange total 13 gallons. 4) Red, blue and orange total 9 gallons. How many gallons of orange paint are left? Answer with a natural number.