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probablity

by [email protected] » Wed Jun 30, 2010 6:57 pm
A class consists of 100 students, 25 of them are girls and 75 boys; 20 of them are rich and remaining poor; 40 of them are fair complexioned. The probability of selecting a fair complexioned rich girl is:

A. 0.05
B. 0.04
C. 0.02
D. 0.08
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by 4GMAT_Mumbai » Wed Jun 30, 2010 7:48 pm
Hi,

This question tests the knowledge of 'Independent events'. If two events A and B are independent; the probability of A and B occurring simultaneously equals the probability of A times the probability of B.

In this case, when one person is chosen from the class, let the events A, B and C be defined as follows

A - Event of choosing a fair person; P(A) = 0.4

B - Event of choosing a rich person; P(B) = 0.2

C - Event of choosing a girl; P(C) = 0.25

Hence, P(choosing a fair complexioned - rich - girl) = [spoiler]P(A) times P(B) times P(C) = 0.4 times 0.2 times 0.25. Hence, 0.02[/spoiler].

Hope this helps.
Naveenan Ramachandran
4GMAT, Dadar(W) & Ghatkopar(W), Mumbai
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