Question

A symmetrical die is tossed twice. Getting a four is considered to be a success. The mean and variance of number of successes are

• A. $\frac{2}{3},\frac{5}{18}$
• B. $\frac{1}{3},\frac{5}{18}$
• C. $\frac{1}{3},\frac{7}{18}$
• D. $\frac{2}{3},\frac{7}{18}$

Answer 1

Answer: (B)

$\frac{1}{3},\frac{5}{18}$

Here, $n=2,p=\frac{1}{6},q=\frac{5}{6}$
$\therefore$ mean $=np=\frac{1}{3}$ and variance $=npq=\frac{5}{18}$