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In a nationwide poll, N people were interviewed. If 1/4 of [#permalink]

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02 Nov 2003, 13:41

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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?

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

Bunuel, can you please look at this question. I personally got E for the answer. But after giving it some thought, I started to doubt it. My reasoning goes like this:

Total: 36

Yes to 1: 9 Yes to 1 and Yes to 2: 1/3 * 9 = 3

No to 1: 36-9 = 27 No to 1 No to 2: ? No to 1 Yes to 2: ?

So, I don't know how we can calculate No 1 No to 2. I guess that's what the question asks.

Thank you.

No, the question asks for {No,No}, {No,Yes}, {Yes,No} any combination but {Yes,Yes}: "the number of people interviewed who did NOT answer "yes" to both questions".

If we use your example then: 1/4th of 36 or 9 people answered YES to question 1. Of those, 1/3 answered "yes" to question 2, so 1/3rd of 9 or 3 people answered YES to BOTH question 1 and 2. So YES to both questions answered 3/36=1/12 of N people interviewed and 1-1/12=11/12 of N people interviewed did NOT answer "yes" to both questions.

Can anyone, please, explain, why result is E? And post OA. I am getting completely different result: 2/3N. If there are 1/4N people answered yes to q1 and 1/3 of those answered yes to q2. Thus, people who answered yes to q2 is 1/12. and total no of people ans yes is 1/12+1/4=1/3N.

So, those who answered NO: N-1/3N=2/3N. What do I do wrong? help appreciated.

One of the GMAT tricks. Do not overcomplicate - they ask for the mumber of people who did not answer "yes" to BOTH questions, while you are calculating "not yes for ANY of the 2 questions"

I solved it in a different approach (with a calculated guess):

N/4 says Yes to Q1. So, 3N/4 will say No to Q1.So, the final number has to be >=3N/4.

On looking the choices B and E remains. We cant have 7 in the denominator, so E is the answer

sudzpwc 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

_________________

Want to improve your CR: http://gmatclub.com/forum/cr-methods-an-approach-to-find-the-best-answers-93146.html Tricky Quant problems: http://gmatclub.com/forum/50-tricky-questions-92834.html Important Grammer Fundamentals: http://gmatclub.com/forum/key-fundamentals-of-grammer-our-crucial-learnings-on-sc-93659.html

So first we figure out what proportion of N did answer yes to both questions. 1/3 answered yes to #1 and of those 1/4 answered yes to #2. Thus 1/3 times 1/4=1/12N answered yes to both. Now it is simple subtraction to find those who did not vote yes on both. 11/12N. So the answer should be E.

If you found these comments helpful, please give kudos. Thanks, Skip

Re: In a nationwide poll, N people were interviewed. If 1/4 of [#permalink]

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03 Jan 2015, 02:55

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This is how I did it:

Yes to 2nd No to second Total Yes to 1st...........10................20.............30 No to 1st................................................90 Total.....................................................120

So, I started by picking a number for the total: I picked 120 as a smart number (3*4=12, which are our denominators). Then, 1/4 answered yes to the 1st question, so 120/4=30, which means that 90 must have answered no to 1st question (120-30=90); we don't need this, but it is an easy calculation and creates a complete table, just to be able to check for mistakes in the additions.

The problem also states that 1/3 of those who said yes to question one, said yes to question 2. So, 30/3=10, and as before 30-10=20 people said no to question 2.

At this point, we can already solve the question, since we are looking for those that didn't answer "yes" to both questions. From the table, there were 10 people out of 120 that answered yes to both questions, so 120-10=110 people did not answer yes to both questions.

Answer choice E ends up in 110: 11N/12= 11*120/12= 1320/12= 110.

Re: In a nationwide poll, N people were interviewed. If 1/4 of [#permalink]

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03 Jan 2015, 02:57

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...................Yes to 2nd.........No to second........Total Yes to 1st...........10.....................20..................30 No to 1st..........................................................90 Total...............................................................120

Just readding the table because it wasn't visible before. Hope it will be clear now!

Q1 {N} ------------------------------------------- YES {N/4} NO {3N/4} --------------------- ----------------- yes Q2 no Q2 yesQ2 noQ2 {N/12} {N/6} ???

I always approach these kinds of sums with flowcharts(for eg. #124).Here what we need is denoted by a question mark.i.e. NO on both questions.I don't understand this,we have no idea of how 3N/4 is broken up.Help??
_________________

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

Can anyone, please, explain, why result is E? And post OA. I am getting completely different result: 2/3N. If there are 1/4N people answered yes to q1 and 1/3 of those answered yes to q2. Thus, people who answered yes to q2 is 1/12. and total no of people ans yes is 1/12+1/4=1/3N.

So, those who answered NO: N-1/3N=2/3N. What do I do wrong? help appreciated.
_________________

Can anyone, please, explain, why result is E? And post OA. I am getting completely different result: 2/3N. If there are 1/4N people answered yes to q1 and 1/3 of those answered yes to q2. Thus, people who answered yes to q2 is 1/12. and total no of people ans yes is 1/12+1/4=1/3N.

So, those who answered NO: N-1/3N=2/3N. What do I do wrong? help appreciated.

One of the GMAT tricks. Do not overcomplicate - they ask for the mumber of people who did not answer "yes" to BOTH questions, while you are calculating "not yes for ANY of the 2 questions"

E should be correct

Ok, thanks. So does question asks ("of those") meaning of all people?
_________________

Yes i too go with the answer of 11N/12. The trick here is the number of people who have not answered YES to both questions is not the same as the number of people who have answered NO to both questions. It could be that they had answered YES to only one of the questions or NO to both questions.

Bunuel, can you please look at this question. I personally got E for the answer. But after giving it some thought, I started to doubt it. My reasoning goes like this:

Total: 36

Yes to 1: 9 Yes to 1 and Yes to 2: 1/3 * 9 = 3

No to 1: 36-9 = 27 No to 1 No to 2: ? No to 1 Yes to 2: ?

So, I don't know how we can calculate No 1 No to 2. I guess that's what the question asks.

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