The school of business has 3 fax machines. The toner in each machine needs to be changed after about 5 hours of use. There is one unit secretary who is responsible for the fax machine maintenance. It takes him 15 minutes to replace the toner cartridge. What is the probability that 2 fax machines need toner at the same time?

That is an indeterminant question, as we do not know the amount of fax time used of each machine and it certainly won't be equal. However, based on whats given you could say

Step-by-step explanation:

5 hrs. use / 0.25 service time = 20 / 3 machines = 6.67. Probability of needing to service 2 machines simultaneously is: 1/6.67 = 15%.