23. Telephone calls from an office are monitored and found to have a mean duration of 452 s and a standard deviation of 123 s. Determine (a) (b) the probability of the length of a call being between...

Extracted text: 23. Telephone calls from an office are monitored and found to have a mean duration of 452 s and a standard deviation of 123 s. Determine (a) (b) the probability of the length of a call being between 300 s and 450 s. the proportion of calls likely to last for more than 700 s.