Purple paint is made by mixing red paint and blue paint in the ratio 2 : 3. If 15 litres of blue paint is used, how much red paint will be needed?

10 liters

Step-by-step explanation:

Red : Blue

2 3

We want 15 blue liters

15/3 = 5

Multiply each term by 5

Red : Blue

2*5 3*5

10 : 15

Because they are in the ratio 2:3 we'll call red and blue paint 2x and 3x respectively. We know that there are 15 liters of blue paint which means that 3x = 15. Solving for x we get x = 5. Since red paint is denoted by 2x it would be 2 * x = 2 * 5 = 10.