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Students that attended the science fair on all three days

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by gmattesttaker2 » Sun Nov 03, 2013 4:25 pm
Hello,

I was just wondering how to solve the following using the Double Set Matrix:

A certain high school with a total enrollment of 900 students held a science fair for three days last week. How many of the students enrolled in the high school attended the science fair on all three days?

(1) Of the students enrolled in the school, 30 percent attended the science fair on two or more days.
(2) Of the students enrolled in the school, 10 percent of those that attended the science fair on at least one day attended on all three days

OA: E

Thanks a lot,
Sri
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Source: — Data Sufficiency |
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by theCodeToGMAT » Sun Nov 03, 2013 8:08 pm
Total enrollment = 900 students

To find: Number of Students enrolled

Statement 1:
30% attended on two or more days
We cannot tell how enrolled for all three days..
INSUFFICIENT

Statement 2:
10% at least 1 day..
We do not have any definite figure for the number of students enrolled for all threee days.
INSUFFICIENT

Combining...
We still don't have the Number of students enrolled for 3 days
INSUFFICIENT
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by mevicks » Mon Nov 04, 2013 4:15 am
gmattesttaker2 wrote:Hello,

I was just wondering how to solve the following using the Double Set Matrix:
I think we cannot solve this question with the double set matrix approach as we don't have overlapping sets here which can ultimately be summed up to reach a final total i.e. we need mutually exclusive options (a, not a, b not b etc).
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by Brent@GMATPrepNow » Mon Nov 04, 2013 7:00 am
gmattesttaker2 wrote:Hello,

I was just wondering how to solve the following using the Double Set Matrix:

A certain high school with a total enrollment of 900 students held a science fair for three days last week. How many of the students enrolled in the high school attended the science fair on all three days?

(1) Of the students enrolled in the school, 30 percent attended the science fair on two or more days.
(2) Of the students enrolled in the school, 10 percent of those that attended the science fair on at least one day attended on all three days

OA: E

Thanks a lot,
Sri
To use the Double Matrix Method, we need a population in which each member has exactly two characteristics associated with it.

For example, a group of students in which the two characteristics are:
- attended day 1 of the fair or didn't attend day 1
- attended day 2 of the fair or didn't attend day 2
Since the population in your question has a third characteristic (attended day 3 of the fair or didn't attend day 3), we cannot use the Double Matrix method.

Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
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