A concrete mix uses 2 parts cement to 5 parts sand. How much cement is needed to make 63 cubic feet of mix?

Correct answer to question 35 (Arithmetic Reasoning): 18 cubic feet

Method

The mix divides into 2 + 5 = 7 parts, and cement is 2 of them. One part is 63 divided by 7, or 9 cubic feet, so the cement comes to 2 x 9 = 18 cubic feet. Using 2/5 instead of 2/7 is the common error.