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DS on Probability

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DS on Probability

by hrishikesh05 » Sat Dec 13, 2008 1:21 am
If each of the students in a certain mathematics class is either a junior or a senior, how
many students are in the class?
(1) If one student is to be chosen at random from the class to attend a conference,
the probability that the student chosen will be a senior is 4/7.
(2) There are 5 more seniors in the class than juniors




OA C
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Source: — Data Sufficiency |
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by hrishikesh05 » Sat Dec 13, 2008 1:22 am
I am getting A for this one
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by NicoFalcon » Sat Dec 13, 2008 5:47 am
Class= J(jrs)+S(srs)

(1) S= 4/7 of the total, so S/(S+J)=4/7. INSUFF

(1) S=J+5. INSUFF

(1)+(2) S/(S+J)= 4/7 (1)

Replacing (2) into (1)
(J+5)/(J+(J+5))=4/7
SUFF

Answer C

There are 15 Junior and 20 Senior students in the class. Total q is 35
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