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In a particular state, 70 percent of the counties. . .

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In a particular state, 70 percent of the counties. . .

by Vincen » Fri Sep 22, 2017 9:53 am
In a particular state, 70 percent of the counties received some rain on Monday, and 65 percent of the counties received some rain on Tuesday. No rain fell either day in 25 percent of the counties in the state. What percent of the counties received some rain on Monday and Tuesday?

(A) 12.5%
(B) 40%
(C) 50%
(D) 60%
(E) 67.5%

The OA is D.

This PS question with percentages confuse me. I need some help. Thanks.
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by [email protected] » Sat Sep 23, 2017 10:12 am
Hi Vincen,

This question is an example of a standard Overlapping Sets question. There are a couple of different ways that you can solve it, including the Overlapping Sets formula and the Tic-Tac-Toe Board/matrix grid. Here's how you can use the formula:

Total = (Group 1) + (Group 2) - (Both) + (Neither)

In this prompt, Group 1 is the counties that received rain on Monday and Group 2 is the counties that received rain on Tuesday.

100% = (70%) + (65%) - (Both) + (25%)
100% = 160% - Both
Both = 60%

Final Answer: D

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by Jeff@TargetTestPrep » Mon Dec 18, 2017 3:29 pm
Vincen wrote:In a particular state, 70 percent of the counties received some rain on Monday, and 65 percent of the counties received some rain on Tuesday. No rain fell either day in 25 percent of the counties in the state. What percent of the counties received some rain on Monday and Tuesday?

(A) 12.5%
(B) 40%
(C) 50%
(D) 60%
(E) 67.5%
We can use the following formula:

100 = rain on Monday + rain on Tuesday - rain on both + rain on neither

100 = 70 + 65 - both + 25

Both = 60

D

Jeffrey Miller
Head of GMAT Instruction
[email protected]

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