Question 1199970
you can use the following calcuator to solve this:
<a href = "https://davidmlane.com/hyperstat/z_table.html" target = "_blank">https://davidmlane.com/hyperstat/z_table.html</a>



the mean is 80 minuts and the standard dviation is 10 minutes.


a.) What is the probability of completing the examination in 1hour or less.


<img src = "http://theo.x10hosting.com/2023/012904.jpg">


the probability is equal to .0228.


b.) What is the probability that a student will complete the exam in more than 60minutes but less than 75 minutes.


<img src = "http://theo.x10hosting.com/2023/012905.jpg">


the probability is .2858.


c.) Assume that the class has 60students and the examination period is 90minutes, how many student do you expect to be unable to complete the exam in the allotted time.


<img src = "http://theo.x10hosting.com/2023/012906.jpg">


the probability is .1587 * 60 = 9.522.
you would expect the number of students to be equal to 10.

 
if you need to know how to do this using z-scores, let me know.
theo