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1/3 +1/2 - 5/6 + 1/5 + 1/4 - 9/20 =

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by DavidG@VeritasPrep » Sun Dec 10, 2017 11:03 am
M7MBA wrote:1/3 +1/2 - 5/6 + 1/5 + 1/4 - 9/20 =

A. 0
B. 2/15
C. 2/5
D. 9/20
E. 5/6

The OA is A.

Experts, is there a fast way to solve this? There are many fractions.
Split it into two pieces, each of which allows for an easy calculation for your common denominator
Piece One: 1/3 + 1/2 - 5/6
3/6 + 2/6 - 5/6 = 5/6 - 5/6 = 0

Piece Two: 1/5 + 1/4 - 9/20
4/20 + 5/20 - 9/20 = 9/20 - 9/20 = 0

0 + 0 = 0. The answer is A
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by GMATGuruNY » Mon Dec 11, 2017 3:56 am
M7MBA wrote:1/3 +1/2 - 5/6 + 1/5 + 1/4 - 9/20 =

A. 0
B. 2/15
C. 2/5
D. 9/20
E. 5/6
Set the equation equal to x and multiply by the LCM of the denominators (60):

x = 1/3 +1/2 - 5/6 + 1/5 + 1/4 - 9/20

60x = 60(1/3 +1/2 - 5/6 + 1/5 + 1/4 - 9/20)

60x = 20 + 30 - 50 + 12 + 15 - 27

60x = 50 - 50 + 27 - 27

60x = 0

x = 0.

The correct answer is A.
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by Brent@GMATPrepNow » Mon Dec 11, 2017 8:02 am
M7MBA wrote:1/3 +1/2 - 5/6 + 1/5 + 1/4 - 9/20 =

A. 0
B. 2/15
C. 2/5
D. 9/20
E. 5/6
For integers x and y, we can say: 1/x + 1/y = (x + y)/xy

Applying this property, we get:
1/3 +1/2 - 5/6 + 1/5 + 1/4 - 9/20 = (3 + 2)/(3)(2) - 5/6 + (5 + 4)/(5)(4)- 9/20
= 5/6 - 5/6 + 9/20 - 9/20
= 0
= A

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