Question

The mean of the numbers obtained on throwing a die having written 1 on three faces, 2 on two faces and 5 on one face is

• A. 1
• B. 2
• C. 5
• D. $\frac{3}{8}$

Answer 1

Answer: (B)

2

Answer 2

The correct option is(B): 2

Let X be the random variable representing a number on the die. The total number of observations is six.

P(X=1)=$\frac{3}{6}=\frac{1}{2}$

P(X=2)=$\frac{2}{6}=\frac{1}{3}$

P(X=5)=$\frac{1}{6}$

Therefore, the probability distribution is as follows.

X	1	2	5
P(X)	$\frac{1}{2}$	$\frac{1}{3}$	$\frac{1}{6}$

Mean = E(X) =∑pixi

=$\frac{1}{2}×1+\frac{1}{3}×2+\frac{1}{6}.5$

$=\frac{1}{2}+\frac{2}{3}+\frac{5}{6}$

=$\frac{3+4+5}{6}$=$\frac{12}{6}$

=2

so the correct answer is B.