Manhattan prac test question

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Junior | Next Rank: 30 Posts
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Manhattan prac test question

by steveyb » Tue Jan 06, 2009 5:33 pm
In a group of 68 students, each student is registered for at least one of three classes – History, Math and English. Twenty-five students are registered for History, twenty-five students are registered for Math, and thirty-four students are registered for English. If only three students are registered for all three classes, how many students are registered for exactly two classes?

a) 13
b) 10
c) 9
d) 8
e) 7

OA: B
Source: — Problem Solving |

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by cramya » Tue Jan 06, 2009 5:47 pm
Apply 3 sets formula:

Total = group1+ group2+group3 + None - grp 1 and 2 - grp 2 and 3 - grp 3 and 1 - 2 grp (1 and 2 and 3)

68 = 25 + 25 + 34 + 0 - grp 1 and 2 - grp 2 and 3 - grp 3 and 1 - 2(3)

grp 1 and 2 + grp 2 and 3 + grp 3 and 1 = 25+25+34-68-6
= 10

Hope this helps! Let me know if u still have questions.

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by steveyb » Tue Jan 06, 2009 6:12 pm
cramya wrote:Apply 3 sets formula:

Total = group1+ group2+group3 + None - grp 1 and 2 - grp 2 and 3 - grp 3 and 1 - 2 grp (1 and 2 and 3)

68 = 25 + 25 + 34 + 0 - grp 1 and 2 - grp 2 and 3 - grp 3 and 1 - 2(3)

grp 1 and 2 + grp 2 and 3 + grp 3 and 1 = 25+25+34-68-6
= 10

Hope this helps! Let me know if u still have questions.
yeah this formula is much better than the crazy explanation Manhattan tried to give, thanks... unfortunately I'm realizing that doing well on the gmat means not just knowing how to do math but how to do it fast..

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by cramya » Tue Jan 06, 2009 6:14 pm
I'm realizing that doing well on the gmat means not just knowing how to do math but how to do it fast..

Coudnt have said better! We can solve even a tough question under no time pressure but with it we dont know. Hope we can...


Good luck!