Question

a pizza delivery shop averages 21 minutes per delivery with a standard deviation of 3 minutes. what is the probability that a pizza takes less than 15 minutes to be delivered?

Answer 1

We have the mean, μ = 21 and the standard deviation, σ = 3

We want P(X<15)

Standardizing gives:

P(X<15) = P(Z<(15-21)/3)
P(X<15) = P(Z< -2) ⇒ When the value of the z-score is negative, we will read the value of z<2 on the z-table then subtract the answer from 1

P(X<15) = 1 - P(Z<2)
P(X<15) = 1 - 0.9772
P(X<15) = 0.0228

the probability that pizza takes less than 15 minutes to be delivered is 0.0228 = 2.28%

Round answer as needed