Class A is twice as big as Class B. Class A is also a third the size of Class C. If Class B has 20 people in it, how many people are in Class C? Let's answer step by step:
Class A is twice the size of Class B, so Class A = 2 * size of Class B. If Class B has 20 people Class A has 20 * 2 = 40 people. Since Class A is also 1 / 3 the size of Class C then Class A = 1 / 3 * Class C. This means 40 = 1 / 3 * Class C. Thus the size of Class C is 3 * 40 = 120 people. The answer: 120.