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# Is the probability of choosing a student in class X who has scored

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Math Expert
Joined: 02 Aug 2009
Posts: 5360

Kudos [?]: 6146 [0], given: 121

Is the probability of choosing a student in class X who has scored [#permalink]

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27 Nov 2017, 08:12
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46% (00:49) correct 54% (01:13) wrong based on 26 sessions

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Is the probability of choosing a student in class X who has scored more than 50% greater than $$\frac{1}{4}$$?

(1) probability of choosing a boy in class X who has scored more than 50% is $$\frac{1}{2}$$.
(2) probability of choosing a girl in the class X is $$\frac{2}{5}$$.

[Reveal] Spoiler: OA

_________________

Absolute modulus :http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372
Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html

Kudos [?]: 6146 [0], given: 121

Math Expert
Joined: 02 Aug 2009
Posts: 5360

Kudos [?]: 6146 [1], given: 121

Is the probability of choosing a student in class X who has scored [#permalink]

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27 Nov 2017, 17:44
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chetan2u wrote:
Is the probability of choosing a student in class X who has scored more than 50% greater than $$\frac{1}{4}$$?

(1) probability of choosing a boy in class X who has scored more than 50% is $$\frac{1}{2}$$.
(2) probability of choosing a girl in the class X is $$\frac{2}{5}$$.

so Q is :- P of picking a student scoring more than 50% >1/4??

lets see the statements

(1) probability of choosing a boy in class X who has scored more than 50% is $$\frac{1}{2}$$.
insuff

(2) probability of choosing a girl in the class X is $$\frac{2}{5}$$
again info only about girls but doesn't tell us that how many girls score >50%
insuff

Combined
Easy to chose E as the numbers of both not known..
But always solve -
statement II tells us that girls are $$\frac{2}{5}$$ , so boys are $$\frac{3}{5}$$
statement I tells us that 1/2 of boys scored more than 50%
so ATLEAST $$\frac{1}{2}*\frac{3}{5}=\frac{3}{10}$$ scored more than 50%, even if none of the girls scored above 50%
$$\frac{3}{10}>\frac{1}{4}$$, so ans is always YES
suff

C
_________________

Absolute modulus :http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372
Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html

Kudos [?]: 6146 [1], given: 121

Intern
Joined: 20 Nov 2017
Posts: 6

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

Re: Is the probability of choosing a student in class X who has scored [#permalink]

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27 Nov 2017, 17:59
chetan2u wrote:
chetan2u wrote:
Is the probability of choosing a student in class X who has scored more than 50% greater than $$\frac{1}{4}$$?

(1) probability of choosing a boy in class X who has scored more than 50% is $$\frac{1}{2}$$.
(2) probability of choosing a girl in the class X is $$\frac{2}{5}$$.

so Q is :- P of picking a student scoring more than 50% >1/4??

lets see the statements

(1) probability of choosing a boy in class X who has scored more than 50% is $$\frac{1}{2}$$.
insuff

(2) probability of choosing a girl in the class X is $$\frac{2}{5}$$
again info only about girls but doesn't tell us that how many girls score >50%
insuff

Combined
Easy to chose E as the numbers of both not known..
But always solve -
statement II tells us that girls are $$\frac{2}{5}$$ , so boys are $$\frac{3}{5}$$
statement I tells us that 1/2 of boys scored more than 50%
so ATLEAST $$\frac{1}{2}*\frac{3}{5}=\frac{3}{10}$$ scored more than 50%, even if none of the girls scored above 50%
$$\frac{3}{10}>\frac{1}{4}$$, so ans is always YES
suff

C

OMG, i have restudied it in mathematics

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

Re: Is the probability of choosing a student in class X who has scored   [#permalink] 27 Nov 2017, 17:59
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