23.Telephone calls from an office are monitored and found to have a mean duration of 452 s and a standarddeviation of 123 s. Determine (a)the probability of the length of a call being between 300 s...

23.Telephone calls from an office are monitored and found to have a mean duration of 452 s and a standarddeviation of 123 s. Determine
(a)the probability of the length of a call being between 300 s and 450 s.

(b)the proportion of calls likely to last for more than 700 s.