Answer
$P(X\geq22.1)=0.0015$
Since $P(X\geq22.1)\lt0.05$, it is unusual.
This result contradicts the BK's rate of 20 cars every hour between 12:00 noon and 1:00 P.M. But, unusual is not impossible.
Work Step by Step
$μ_{X ̅}=20~cars$ and $σ_{X ̅}=0.707~cars$
Let's find the z-score for 22.1:
$z=\frac{X-μ}{σ}=\frac{22.1-20}{0.707}=2.97$
According to Table V, the area of the standard normal curve to the left of z-score equal to 2.97 is 0.9985.
But, we want the area of the standard normal curve to the right of z-score equal to 2.97:
$1-0.9985=0.0015$
$P(X\geq22.1)=0.0015\lt0.05$. It is an unusual event.
