Jeff Miller

GMAT OFFICIAL GUIDE PS – 1/3 + 1/2 – 5/6 + 1/5 + 1/4…

1/3 + 1/2 – 5/6 + 1/5 + 1/4…

Solution:

We need to determine the result of 1/3 + 1/2 – 5/6 + 1/5 + 1/4 – 9/20

Let’s add the given fractions in two groups. In the group of the first three fractions, notice that 1/3 and 1/2 share a common denominator of 6 with 5/6. 
 
1/2 + 1/3 = 3/6 + 2/6 = 5/6

Thus, 5/6 – 5/6 = 0

Looking at the 2nd group of the fractions (1/5, 1/4, and 9/20), notice that 1/5 and 1/4 share a common denominator of 20 with 9/20. 
 
1/5 + 1/4 = 4/20 + 5/20 = 9/20

Thus, 9/20 – 9/20 = 0.

Thus, the result of 1/3 + 1/2 – 5/6 + 1/5 + 1/4 – 9/20 is 0.

Answer: A 

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