The mean of a normal probability distribution is 440; the standard deviation is 8.

Question

A: About 95% of the observations lie between what two values?
B: Practically all of the observations lie between what to values?

Answer 1

A: 2 s.d. below and 2 s.d. above the mean
... [440 - (2 * 8)] and [440 + (2 * 8)]

B: 3 s.d. below and 3 s.d. above the mean
... [440 - (3 * 8)] and [440 + (3 * 8)]