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# how to solve with martix method

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Intern
Joined: 10 Jan 2011
Posts: 21
Location: India
Schools: ISB, IIM-A
WE 1: 4 yrs in finance
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how to solve with martix method [#permalink]

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08 Mar 2011, 09:53
00:00

Difficulty:

(N/A)

Question Stats:

75% (02:10) correct 25% (02:55) wrong based on 4 sessions

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In a group of 52 persons, 16 drink tea but not coffee, & 33 drink tea . how many drink coffee not tea??

a) 90
b) 70
c) 30
d) 15
[Reveal] Spoiler: OA

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Rahul

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Status: Matriculating
Affiliations: Chicago Booth Class of 2015
Joined: 03 Feb 2011
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Re: how to solve with martix method [#permalink]

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08 Mar 2011, 10:03
What is the number that drinks neither tea nor coffee. I think data is missing.

ITMRAHUL wrote:
In a group of 52 persons, 16 drink tea but not coffee, & 33 drink tea . how many drink coffee not tea??

a) 90
b) 70
c) 30
d) 15
Manager
Joined: 14 Feb 2011
Posts: 196
Followers: 4

Kudos [?]: 101 [0], given: 3

Re: how to solve with martix method [#permalink]

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08 Mar 2011, 10:12
ITMRAHUL wrote:
In a group of 52 persons, 16 drink tea but not coffee, & 33 drink tea . how many drink coffee not tea??

a) 90
b) 70
c) 30
d) 15

Are you sure, the question is complete and data is correct? How can answer be 90 if it talks of a group of 52 persons? Please recheck.
Intern
Joined: 10 Jan 2011
Posts: 21
Location: India
Schools: ISB, IIM-A
WE 1: 4 yrs in finance
Followers: 0

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

Re: how to solve with martix method [#permalink]

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08 Mar 2011, 11:02
Soln for the problem given is

n(a)=33 represents ( persons drink tea)
n(aUb)=52 represents( total persons)
n(a-b)=16 represents persons drink tea not coffee

n(a^b)=n(a)-n(a-b) {^ represents inverse of Union i.e intersection, mean drinks both coffee & tea)

=33-16

n(aUb)= n(a-b) + n (a^b) + n (b-a)

=> n(b-a)= 52-16-17

=19
its ( 19) by mistake i typed it 90 (sorry everyone) (
though i knw how to solve with these formulas but i tried to solve with matrix but could find soln.
anyway guys above is soln
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Rahul

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Re: how to solve with martix method [#permalink]

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08 Mar 2011, 18:37
i got 19.

i was breaking my head over this , thinking how can answer be 90..Then i saw your correction in the bottom
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Re: how to solve with martix method [#permalink]

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08 Mar 2011, 22:19
A Venn diagram can make it very clear (I don't know how to draw one online though )

# of people who drink both Tea and coffee = 33 - 16 = 17

x = # of people who drink only coffee

52 = 17 + 16 + x

=> x = 52 - 33 = 19
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Re: how to solve with martix method   [#permalink] 08 Mar 2011, 22:19
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