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
