2012-04-13 09:00:38

If a + b = 18, b + c = 45, and a + c = 39, what is the average of a, b, and c?

The correct answer is 17

Explanation: Start by combining the three equations into one equation involving a, b, and c. Do this by adding up the equations:

a + b = 18
b + c = 45
a + c  = 39
2a + 2b + 2c = 102

This means that 2(a + b + c) = 102, which means a + b + c = 51 (since 102/2 is 51). The question asks for the average of a, b, and c, and to find an average, you simply need to divide the sum of the terms by the number of terms. Thus, take 51 (the sum of a, b, and c) and divide it by 3 (the number of terms): 51/3 = 17.