At a two-day seminar, 90 percent of those registered attended the semi

The answer is E. We do not have enough information to solve this problem, because we don't know what percentage the overlap of attendance was between the two days. For example, all 80% that attended the second day also attended the first day. This would result in 10 % of people who didn't attend either day. however, if only 7/8 of the 80% that attended the second day also attended the first day, then you'd have 0% that attended either day. Since we could have multiple values that fulfill this, we cannot answer the question.

Statement 1 is irrelevant.

I am getting E on this one.

1) INSUFFICIENT: This tells us that 900 people attended the seminar on the first day. 100 people did not atttend. But we know nothing about day 2.

2) INSUFFICIENT: We don't have any numbers to calculate how many people actually went to the seminar on both days.

Together: We know that 100 people did not attend on day 1 and that 200 people did not attend on day 2. But these could be unique people, so that 0% did not attend the seminars on either day. It could also be that the 100 people who did not attend on day 1 did not attend on day 2. So together insufficient.

A venn diagram would only be useful if we knew something about the overlap, ie how many people who went to the seminar on day 1 that also went on day 2. Since we have nothing on that, I am thinking E.

Can somebody help me to solve this question through matrix ? I was unable to form matrix. Please help me.

Total = Group 1 + Group 2 - Both + Neither, in our case we have
1000 = 900 + 800 - Both + Neither.
Since we are still left with two variables (B and N), the correct answer is E.
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remember, the more approaches you have to these problems, the better off you will be on test day; the most important thing to do in a situation like this one -- in which there are multiple ways to solve the same problem -- is to become familiar with ALL of those methods, not to spend time worrying about which is "better" or "easier".

Let number of registered voters =x
Attendees on first day=0.90x
% of registered did not attending either day=?

Statement 1- insufficient. Total attendees 1000, which is x. so attendees on first day is 900. This means 100 attendees are left but gives no information of how many of the registered attended the second day or how many did not attend either day. A and D eliminated

Statement 2- insufficient. Attendees on second day=80% of x (.80x). This alone gives no information about total attendees or those who did not attend either day. B eliminated.

Taking both statements together gives information about the attendees on both days but gives no figure for the registered attending both day (overlapped figure) so we cannot find those who did not attend the seminar on either day. C eliminated.
Correct answer E.

The formula to use :
n(AUB) = n(A)+n(B) - n(AnB) + X(percent of those registered did not attend the seminar on either day)
1000=900+800-n(AnB) + X . So, without knowing the value of n(AnB), we cannot find the value of X
. So, E is our answer.



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