The Solution:
The sample space (S) for the waiting time, rounded to minutes is given as below:
[tex]S=\mleft\lbrace12,13,14,15,16,17,18\mright\rbrace[/tex]A. To find the probability that Andrew waits for 15 minutes, we have
[tex]\text{prob}(15\text{ minutes) =}\frac{\text{ number of 15}}{\text{ total number of sample}}=\frac{1}{7}=0.14286\approx0.143[/tex]B. The probability that Andrew waits between 13 and 15 minutes is
[tex]\text{Prob( between 13 and 15) }=\frac{\text{ number between 13 and 15}}{\text{ total number of sample}}=\frac{3}{7}=0.42857\approx0.429[/tex]Therefore, the correct answers are:
A. 0.143
B. 0.429