Question

$\frac{2}{3}$ of students of a class are boys and the restgirls. It is given that the probability of a girl getting $1$st class is $0.25$ and the same for a boy is $0.28$. From that class a student is selected atrandom. The probability that the student is a $1$st class student

• A. $0.25$
• B. $0.26$
• C. $0.27$
• D. $0.28$

Answer 1

Answer: (C)

$0.27$

Let $B$ stand for boys and $G$ for girls.

Given, $P\left(B\right)=\frac{2}{3}$
Hence
$P\left(G\right)=1-\frac{2}{3}=\frac{1}{3}$

Thus, the required probability will be
$=\frac{0.28\times 2}{3}+\frac{0.25\times 1}{3}$
$=\frac{1}{3}[0.56+0.25]$
$=\frac{0.81}{3}$
$=0.27$