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is this question complete?

by r_walid » Fri Jan 23, 2009 9:21 pm
i couldn't solve this problem, is the info it gives incomplete or am i missing smthg?

in a poll, P ppl were asked 2 questions. If 2/5 said yes to Q1, and of those 1/3 also answered yes to Q2, which of the following represents the number of ppl polled who did not answer yes to both question?
2/15P
3/5P
3/4P
5/6P
13/15P

If you know how to solve it ,please explain how. otherwise, please let me know if you think there is not enough info to help us solve the problem.
the thing is that i can obtain of course the fraction of ppl who said yes o q 1 and Q 2 and of those who said no to Q1. But I don't know either distribution of the latter (3/5 P) who said no to Q1 but who said either yes or no. we have no info on that distribution and that's where i think we're missing an info.

thank you
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by gaggleofgirls » Fri Jan 23, 2009 10:46 pm
I think there is enough information...

You either need to figure out how many people answered Yes/No, No/Yes and No/No or you just need 1- the number of people who answered Yes/Yes

2/5 of the people answered Yes to the first question. 1/3 of this 2/5 also answered Yes to the second question, so 1/3 * 2/5 = 2/15.

2/15 answered Yes to both, so 13/15p did not answer yes to both.

Answer is E.

-Carrie
Last edited by gaggleofgirls on Fri Jan 23, 2009 11:21 pm, edited 1 time in total.
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by DanaJ » Fri Jan 23, 2009 10:59 pm
Man I got so tangled up in this thing and I miss-read the instructions.... People who did not answer yes to both questions = people who answered "No" at least once. This means people who answered:
No to Q1 and Yes to Q2
No to Q1 and No to Q2
Yes to Q1 and No to Q2

This fraction of people is actually (1 - fraction of people who answered Yes to both questions):

Since 1/3 of those who said Yes to Q1 also said Yes to Q2, that means that people who said Yes to both questions represent 1/3*2/5 = 2/15. That means that the fraction you are looking for is 1 - 2/15 = 13/15 P
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by yvichman » Sat Jan 24, 2009 11:04 am
in a poll, P ppl were asked 2 questions. If 2/5 said yes to Q1, and of those 1/3 also answered yes to Q2, which of the following represents the number of ppl polled who did not answer yes to both question?
2/15P
3/5P
3/4P
5/6P
13/15P

I got the same answer...but with these types of questions I like to use real numbers, not fractions. It helps me understand the question easier.
2/5 said yes to Q1 and 1/3 of those who said yes to Q1 also said yes to Q2.

I picked 15 as P b/c its divisible by both 5 and 3

Those that Said yes to Q1= 2/5 of the 15 = 6
Those that Said yes to Q2= 1/3 of of those who said yes to Q1= 2

so 2/15 said yes to both... all the others said no to at least one of the questions 13/15P
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