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by KapilKapoor » Mon Sep 03, 2012 10:31 pm
In a nationwide poll, N people were interviewed. If 1/4 of them answered "yes" to question 1, and of those, 1/3 answered "yes" to question 2, which of the following expressions represents the number of people interviewed who did not answer "yes" to both questions?
a. N/7
b. 6N/7
c. 5N/12
d. 7N/12
e. 11N/12

OA is e.

I did not understand, where to start the question. Please help.

Thanks
Kapil
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Source: — Problem Solving |

by neelgandham » Mon Sep 03, 2012 10:53 pm
Number of people interviewed = N
Number of people who answered first question correct = N/4
Number of people who answered first question and second question correct = (1/3)*(N/4) = (N/12)
Number of people who didn't answer YES to both the questions = N - Number of people who answered both the questions correct = N = (N/12) = 11N/12
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by Anurag@Gurome » Mon Sep 03, 2012 11:58 pm
KapilKapoor wrote:In a nationwide poll, N people were interviewed. If 1/4 of them answered "yes" to question 1, and of those, 1/3 answered "yes" to question 2, which of the following expressions represents the number of people interviewed who did not answer "yes" to both questions?
a. N/7
b. 6N/7
c. 5N/12
d. 7N/12
e. 11N/12

OA is e.

I did not understand, where to start the question. Please help.

Thanks
Kapil

Number of people who answered "yes" to Q1 = N/4
Of the people who answered "yes" to Q1, number of people who answered "yes" to Q2 = (1/3)(N/4) = N/12
So, number of people who answered "yes" to Q1 and Q2, both = N/12
Therefore, number of people who did not answered "yes" to Q1 and Q2, both = 1- N/12 = [spoiler]11N/12 [/spoiler]

The correct answer is E.
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by KapilKapoor » Tue Sep 04, 2012 8:53 am
Thanks both of you for short and simple solution. I don't why i could not solve such a simple question!!!
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by GMATGuruNY » Tue Sep 04, 2012 10:15 am
In a nationwide poll, N people were interviewed. If 1/4 of them answered "yes" to question 1, and of those, 1/3 answered "yes" to question 2, which of the following expressions represents the number of people interviewed who did NOT answer "yes" to both questions?

A) N/7

B) 6N/7

C) 5N/12

D) 7N/12

E) 11N/12
Let N=12.
Number who answered YES to question 1 = (1/4)*12 = 3.
Of these 3 people, the number who also answered YES to question 2 = (1/3)*3 = 1.
Since only 1 person answered YES to both questions, the number who did not answer YES to both questions = 12-1 = 11. This is our target.

Now we plug N=12 into the answers to see which yields our target of 11.

Only answer choice E works:
11N/12 = (11*12)/12 = 11.

The correct answer is E.
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