Paint is red : blue in a ratio of 2 : 4. If 5 litres of red is used how much blue is used

so since the ratio of red paint to blue paint is 2:4 and you can simplify 2:4 into 1:2 and because 5 liters of paint is used you would have to multiply the 2 from the simplified ratio by 5 so you could get the answer 2*5 and that equals 10