Answer
a) $1.08$ standard deviations below the mean.
b) A car going $10$ mph would be more unusual.
Work Step by Step
a)
$z=\frac{y-\mu}{\rho}=\frac{20-23.84}{3.56}=-1.08$
The answer is $1.08$ standard deviations below the mean.
b)
$z=\frac{y-\mu}{\rho}=\frac{34-23.84}{3.56}=2.85$
$z=\frac{y-\mu}{\rho}=\frac{10-23.84}{3.56}=-3.89$
A car going $10$ mph would be more unusual.
