Marcus reed hits about 90% of all his free throws. you randomly select 15 of his free throws. let the random variable x represent the number of free throws marcus reed hits out of the 15 selected. find the mean, variance, and standard deviation of x.

This is a question of Binomial random variable. From the  information given;

p = 90% = 0.9
n = sample size = 15

Then, the following calculations can be done:

Mean of X = np = 15*0.9 = 13.5 ≈ 14 throws

Variance of X = np(1-p) = 15*0.9(1-0.9) = 1.35 ≈ 2 throws

Standard deviation of X = Sqrt (variance) = Sqrt (1.35) = 1.16 ≈ 2 throws.