A die is rolled 360 times. Find the standard deviation of the number of times a 3 will be rolled.
A) 21.3
B) 50
C) 7.1
D) 5.9

Question

Quizplus · Accepted Answer

The probability of rolling a 3 on one throw of the die is 1/6. The expected number of times a 3 will be rolled in 360 throws is 
E(x) = np = 360 * (1/6) = 60
The variance is 
var(x) = npq = 360 * (1/6) * (5/6) = 50
The standard deviation is the square root of the variance, which is approximately 7.1. Therefore, the correct choice is C.

A Die Is Rolled 360 Times