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Sets Problem

by sampath » Wed Aug 17, 2011 2:36 am
The Mathematics Club in a school held an open house on three afternoons. 115, 75 and 110 students
attended on the first, second and third afternoons respectively. 30 attended only on the first day, 35 on the first and second days. 70 attended the first and the third days and 35 attended on the second and third days. How many attended on all the three days?
(A) 15 (B) 25 (C) 21 (D) 20 (E) 30
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by rppala90 » Wed Aug 17, 2011 5:34 am
n(F) = n(F only) + n(F&S) + n(F&T) - n(F&S&T)
F --> First day.
S --> Second day.
T --> Third day.

[spoiler]115 = 30 + 35 + 70 - n(F&S&T)
n(F&S&T) = 135 - 115 = 20
Hence (D)[/spoiler]
I think info about n(S&T), n(S) and n(T) are not needed to solve this question.
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by chufus » Wed Aug 17, 2011 5:59 am
rppala90 wrote:n(F) = n(F only) + n(F&S) + n(F&T) - n(F&S&T)
F --> First day.
S --> Second day.
T --> Third day.

[spoiler]115 = 30 + 35 + 70 - n(F&S&T)
n(F&S&T) = 135 - 115 = 20
Hence (D)[/spoiler]
I think info about n(S&T), n(S) and n(T) are not needed to solve this question.
Everything seems correct to your approach. Wonder why the other info was mentioned in the question. Doesn't seem like a GMAT question !
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by krishna8143 » Wed Aug 17, 2011 11:05 pm
ans is D 20
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by edvhou812 » Wed Aug 17, 2011 11:27 pm
chufus wrote:
rppala90 wrote:n(F) = n(F only) + n(F&S) + n(F&T) - n(F&S&T)
F --> First day.
S --> Second day.
T --> Third day.

[spoiler]115 = 30 + 35 + 70 - n(F&S&T)
n(F&S&T) = 135 - 115 = 20
Hence (D)[/spoiler]
I think info about n(S&T), n(S) and n(T) are not needed to solve this question.
Everything seems correct to your approach. Wonder why the other info was mentioned in the question. Doesn't seem like a GMAT question !
This is a GMAT question.
I don't know what to say, really. Three minutes to the biggest battle of our professional lives. You find out life's this game of inches, so is football. Because in either game - life or football - the margin for error is so small. I mean, one half a step too late or too early and you don't quite make it. One half second too slow, too fast and you don't quite catch it. I'll tell you this, in any fight it's the guy whose willing to die whose gonna win that inch. That's football guys, that's all it is. Now, what are you gonna do?
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