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

[GMAT 5/18]

Not sure if this is an overlapping sets question, but it seemed to me like it was.

At a two-day seminar, 90 percent of those registered attended the seminar on the first day. What percent of those registered did not attend the seminar on either day?

(1) A total of 1,000 people registered for the two-day seminar

(2) Of those registered, 80 percent attended the seminar on the second day.

[Guest]

Is the answer E?
Clearly, 1) and 2) each by itself is not sufficient to answer.

Combining,
FD-900; SD-800
UNFD-100;UNSC-200

But nothing tells us that the 100 from UNFD are among the 200 in UNSD. So there is not enough info to answer the question.

[GMAT 5/18]

Yes, the answer is E. Thanks for your help.

[dbernst]

To me, this is an overlapping sets problem best solved with a two-circle Venn Diagram. Circle #1 is first day attendants, circle #2 is second day attendants, the overlap is attendants for both days, and Neither is the space outside the diagram.

The information from the original problem plus statement (1) give you the first circle (900). Insufficient to solve for Neither.
The information from the original problem plus statement (2) give you the second circle (800). Also Insufficient to solve for Neither.

Together, you still have no idea how many individuals addended Both days. Since the proper formula for such a situation is
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.

[GMAT 5/18]

Thanks, guys!

[fangming_li]

Since the proper formula for such a situation is
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.

I Think that it should be 2000=900+800-Both+Neither

Because this is a two-day seminar, once you registered,it should be two days. you can show up first day, second day, both or neither.

[tim]

There are still only 1000 people though..

[Viswanathan.harsha]

Instead of the two circles, i did it with the boxes instead. If you do it that way (across the top would be Day 1 and Day 2, and going down would be Attended and Not attended). If you add day 1 (900) and day 2 (800) together, would you get 1700? I understand that there are a total of 1000 people, but if these people can attend again the next day, wouldn't you treat it as 2000 people?

[tim]

no, it's still 1000 people. you have set up your matrix incorrectly. the columns should be (attended day 1) and (did not attend day 1), and the rows should be (attended day 2) and (did not attend day 2). this is the only way to ensure that you have four boxes into which everyone will fit exactly once. remember that on overlapping sets problems, your two columns should be exact opposites of each other, and the same is true for rows. day 1 is not the opposite of day 2..

[Viswanathan.harsha]

That makes much more sense. Thanks, Tim!

[RonPurewal]

That makes much more sense. Thanks, Tim!

glad it helped

[agha79]

i took this this question the following way:

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.

[RonPurewal]

thanks all, for contributing such a variety of solutions. this is the main reason why these forums exist -- they are nice focal point for the many different approaches that can be taken to these problems. (in fact, this is one of the hallmarks of good official problems -- almost all of them can be approached in multiple ways.)

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".
.

[supratim7]

Had a bit of language issue with the stem..

Do all of these have same meaning? Are they asking for the same value?

A: "What percent of those registered did not attend the seminar on either day?"
B: "What percent of those registered did not attend the seminar on both days?"
C: "What percent of those registered attended the seminar neither on the first day nor on the second day?"

[messi10]

A and C are the same.

B is asking for the number of people who have attended the seminar at least on one of the days, but not both the days.