If X is a normal random variable with a standard deviation of 10, then 3X has a standard deviation equal to:
A) 10 .
B) 13 .
C) 30 .
D) 90 .

Question

If X is a normal random variable with a standard deviation of 10, then 3X has a standard deviation equal to: 
A)  10 . 
B) 13 .
C)  30 . 
D) 90 .

Quizplus · Accepted Answer

If X is multiplied by a constant c, then the standard deviation of cX is equal to |c| times the standard deviation of X. Therefore, in this case, the standard deviation of 3X is 3 times the standard deviation of X, which is 3*10=30.

If X Is a Normal Random Variable with a Standard