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?
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 = 
<gadget id="calculator">20*2</gadget>
<output>40</output>
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 = 
<gadget id="calculator">3*40</gadget>
<output>120</output>
120 people.

<result>120</result>