Bunuel wrote:

If 12a + 3b = 1 and 7b – 2a = 9, what is the average (arithmetic mean) of a and b ?

A) 0.1

B) 0.5

C) 1

D) 2.5

E) 5

In order to find the arithmetic mean, we need the value of a+b

P.S In the GMAT, most of the times, this kind of question can be done by a very straightforward

approach. You either have to add or subtract the two statements. Sometimes, you might have

to add twice the second statement to the first statement. Try these combinations before you go

ahead and find individual values for a & b.Here, the simple addition of both the statements will lead us to the answer.

12a + 3b + 7b – 2a = 9 + 1 -> 10(a + b) = 10 -> a + b = 1

Therefore, the average of a and b is \(\frac{a+b}{2} = \frac{1}{2}\) =

0.5(Option B)
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