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# Help me understand this one pls...

Author Message
Manager
Joined: 27 Mar 2010
Posts: 117

Kudos [?]: 15 [0], given: 17

Help me understand this one pls... [#permalink]

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17 Apr 2010, 01:42
00:00

Difficulty:

(N/A)

Question Stats:

100% (00:52) correct 0% (00:00) wrong based on 3 sessions

### HideShow timer Statistics

If 75% of a class answered the 1st question on a certain test correctly, 55% answered the 2nd question on the test correctly and 20% answered neither of the questions correctly, what percent answered both correctly?
10%
20%
30%
50%
65%

Kudos [?]: 15 [0], given: 17

Manager
Joined: 13 Dec 2009
Posts: 127

Kudos [?]: 313 [0], given: 10

Re: Help me understand this one pls... [#permalink]

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17 Apr 2010, 06:38
utin wrote:
If 75% of a class answered the 1st question on a certain test correctly, 55% answered the 2nd question on the test correctly and 20% answered neither of the questions correctly, what percent answered both correctly?
10%
20%
30%
50%
65%

from the question stem: 20% answered neither of the two => 80% answered both the questions.
so, we have
Q1or Q2 = Q1+Q2- Q1&Q2 => Q1&Q2 = Q1+Q2-Q1orQ2
=> Q1&Q2 = 75+55-80 = 50%

Kudos [?]: 313 [0], given: 10

Intern
Joined: 21 Dec 2009
Posts: 18

Kudos [?]: 5 [0], given: 0

Re: Help me understand this one pls... [#permalink]

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17 Apr 2010, 06:47
Formula:
Total = A + B + None - Both

So,

100 = 75 + 55 + 20 - Both
Both = 50%

Thanks

Kudos [?]: 5 [0], given: 0

BSchool Forum Moderator
Joined: 02 Oct 2009
Posts: 587

Kudos [?]: 477 [0], given: 412

GMAT 1: 530 Q47 V17
GMAT 2: 710 Q50 V36
Re: Help me understand this one pls... [#permalink]

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25 Apr 2010, 09:55

Kudos [?]: 477 [0], given: 412

Manager
Joined: 27 Dec 2009
Posts: 164

Kudos [?]: 131 [0], given: 3

Re: Help me understand this one pls... [#permalink]

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25 Apr 2010, 10:01
yes ... fairly easy.

Kudos [?]: 131 [0], given: 3

Re: Help me understand this one pls...   [#permalink] 25 Apr 2010, 10:01
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