Students who have completed a speed reading course have readings speeds that are normally distributed with a mean of 950 words per minute and a standard deviation equal to 220 words per minute.10 students are selected at random.

What is the standard deviation of the number of students who read at less than 850 words per minute?

A. 220

B. 10

C. 2.13

D. 1.46

What is the probability that at the most two of them would read at less than 850 words per minute?

A. 0.22

B. 0.64

C. 0.36

D. 0.78