A couple has 4 children. what is the proability that two of them are boys?
a. 1/4
b. 1/2
c. 1/3
d. 3/8
e. 5/8
a. 1/4
b. 1/2
c. 1/3
d. 3/8
e. 5/8
Answer is D.
4c2 * (1/2)^2 * (1/2)^2
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Children and probability.
Source: Beat The GMAT — Problem Solving |
IMO D
either 2 boys 2 girls
or, 3 boys 1 girl
or, 4 boys
2 boys selected in 4C2 ways
total prob=4C2{(1/2)^2*(1/2)^2 + (1/2)^3 *1/2 + (1/2)^4}
=4C2 * 1/16= 3/8
either 2 boys 2 girls
or, 3 boys 1 girl
or, 4 boys
2 boys selected in 4C2 ways
total prob=4C2{(1/2)^2*(1/2)^2 + (1/2)^3 *1/2 + (1/2)^4}
=4C2 * 1/16= 3/8
The powers of two are bloody impolite!!
