Question

Suppose the mean of the student completed the quiz is 30 minutes. Find the probability of a student completed the quiz in less than 20 minutes.

Answer 1

μ = 30 , standard deviation is not given so let it be $\sigma=5$

$z=\dfrac{X-\mu}{\sigma}$

$P(X<20)=P\left(z<\frac{20-30}{5}\right)=P(z<-2)=0.02275$

Hence, the probability of a student completed the quiz in less than 20 minutes is 0.02275