Week 1 Day 2 Practice for Fractions, Decimals, Percents and Ratios video at 50:55

GRE Quant Problem Solving
1

In a nationwide poll, N people were interviewed. If 14 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?

  1. N/7
  2. 6N/7
  3. 5N/12
  4. 7N/12
  5. 11N/12

My question is according to greg N/4 people answer yes, N/12 answer yes to both questions So people who answer no to both are N - N/12 = 11N/12

My question is how do we know that there are no people who answered No on the Question 1 and Yes in Question 2.

Here N/12 signifies it’s (1/3)rd OF people who answered yes in the first question (N/4). What about people who didn’t answer yes in the first question and answered yes in the second question.

3N/4 answered No in the first question, but I’m not able to figure out how to calculate how many of those (3N/4) answered either yes or no.

Apologies if the explanation is confusing, I can try to explain it further if my point is ambigous

2

Tagging @gregmat to get some answer on this post

3

Yeah, can you provide an example?

4

Hi Hope you’re doing well,

So let’s say there are 12 people 1/4th of them answer yes to the Questions 1 thats 3 people, then 1/3rd OF THOSE people answer yes to Questions which is 1 person. In the video it is concluded that number people who did not answer yes to BOTH the question is (12-1=11 or N - N/12= 11N/12).

However my question is there could be a scenario that some people answered No on the first question and then yes on the 2nd. Those aren’t included in the N/12.

Let A = People who answered yes in Q1 and answered No in Q2
B= People who answered yes to both questions
C= People who answered No in Q1 but answered yes in Q2

Number of people who didn’t answer “yes” to both question = Total - (A) - (B) - (C)

The number N/12, I feel only accounts for scenarios A and B.

5

The problem you originally posted says 14. Was that supposed to say 1/4?

6

We need people who haven’t answered “Yes” to both.
Anyone who says No to 1st question should automatically be included as they didn’t say yes to both questions.
Here 3N/4 includes both scenarios, people who say No to both & people who say No & Yes.
So, even if some say No & then Yes, they would be counted as they said No to first question.

7

Yes I wasn’t able find a way to edit my question. Sorry about the confusion