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pls explian

by krbharat » Sat Apr 17, 2010 1:52 am
In a survey of 150 persons, how many were smokers and drinkers?
(I) 80% of the person surveyed were drinkers
(II) 40% of the smokers were drinkers also

(A) Statement (I) ALONE is sufficient, but statement (II) alone is not sufficient

(B) Statement (II) ALONE is sufficient, but statement (I) is not sufficient

(C) BOTH statements TOGETHER are sufficient, but NEITHER statement alone is sufficient

(D) Each statement ALONE is sufficient

(E) Statements (I) and (II) TOGETHER are NOT sufficient

my Answer : C
Actual Answer : E

source:gmat diagnostic test
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Source: — Data Sufficiency |
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by krbharat » Sat Apr 17, 2010 2:02 am
krbharat wrote:In a survey of 150 persons, how many were smokers and drinkers?
(I) 80% of the person surveyed were drinkers
(II) 40% of the smokers were drinkers also

(A) Statement (I) ALONE is sufficient, but statement (II) alone is not sufficient

(B) Statement (II) ALONE is sufficient, but statement (I) is not sufficient

(C) BOTH statements TOGETHER are sufficient, but NEITHER statement alone is sufficient

(D) Each statement ALONE is sufficient

(E) Statements (I) and (II) TOGETHER are NOT sufficient

my Answer : C
Actual Answer : E

source:gmat diagnostic test
st 1:

(80/100)*150=120 noting about smokers so insuff

st 2:

we dont know what % are smokers so insuff

combining:
120 drinkers
30 smokers
so (30/100)*40=12
hence c.

tell me where i went wrong.
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by akdayal » Sat Apr 17, 2010 3:14 am
You are assuming that rest i.e 20% is smokers. In fact smokers %age are not known.
and hence u can not calculate number of smokers and drinkers
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by Fiver » Sat Apr 17, 2010 5:08 am
krbharat wrote:
krbharat wrote:In a survey of 150 persons, how many were smokers and drinkers?
(I) 80% of the person surveyed were drinkers
(II) 40% of the smokers were drinkers also

(A) Statement (I) ALONE is sufficient, but statement (II) alone is not sufficient

(B) Statement (II) ALONE is sufficient, but statement (I) is not sufficient

(C) BOTH statements TOGETHER are sufficient, but NEITHER statement alone is sufficient

(D) Each statement ALONE is sufficient

(E) Statements (I) and (II) TOGETHER are NOT sufficient

my Answer : C
Actual Answer : E

source:gmat diagnostic test
st 1:

(80/100)*150=120 noting about smokers so insuff

st 2:

we dont know what % are smokers so insuff

combining:
120 drinkers
30 smokers
so (30/100)*40=12
hence c.

tell me where i went wrong.
This one is a teaser.
In such problems always ensure that we know the sample size of the set that either smoke or drink or do both.
In short of the total number of 150, we need to know how many do neither of the above 2 activities and that number becomes our sample size under consideration.

If that number were to be given, then our answer would be B, as statement 2 gives us the size of the intersection.
So the answer would have been 40% of the sample size.
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