In an ordinary 8-hour day, Roto-Drains receives calls for emergency service at an average rate of 1 per hour (otherwise, the calls appear to be random and independent).The owner currently has a crew of technicians capable of handling up to (and including) nine emergencies per day.She is considering expanding the crew.If she wants to ensure that there is less than a 5% chance that the crew won't be able to handle the emergency load, she will need a crew that can handle up to (and including) how many emergencies per day.
A)13
B)12
C)15
D)11
E)10

Question

Quizplus · Accepted Answer

The average number of calls per day is 8. The standard deviation is the square root of 8, which is 2.83. To ensure that there is less than a 5% chance that the crew won't be able to handle the emergency load, the crew must be able to handle up to 8 + 2.83 * 1.645 = 13.3 emergencies per day.

In an Ordinary 8-Hour Day, Roto-Drains Receives Calls for Emergency