Answer:
Average waiting time = 7.5 minutes
Explanation:
UTD private secretary can type the number of letters = 4 per hour by each.
By professor, the letter generated = 3 per hour by each
Thus by pooling the average time will be the time that comes by dividing the one hour with total letters in an hour.
Use the below formula:
Average waiting time = Minutes in one hour / total letters
Average waiting time = 60 / 8
Average waiting time = 7.5 minutes