Suppose that the annual rainfall in Ferndale, California, is known to be normally distributed, with a mean of 32 inches and a standard deviation of 4 inches. About 0.1% of the time, the annual rainfall will be less than how many inches?
A) 20 inches
B) 44 inches
C) 24 inches
D) 40 inches
E) 32 inches

Question

Quizplus · Accepted Answer

The z-score corresponding to the bottom 0.1% of a normal distribution is approximately -3.09. Using the formula X = μ + zσ, where μ = 32 and σ = 4, we find X = 32 + (-3.09)(4) = 19.64 inches, which is closest to 20 inches.

Suppose That the Annual Rainfall in Ferndale, California, Is Known