If 'X' is a random variable which denotes 'duration of pregnancy in humans', then .

(a) Required to find

=

= (put the values)

(b) Required to find

= (put the value)

(c) Find Q's such that , while is

"Standardization" has been done in (a) and (b); Z is a standard normal variate and denotes the CDF of a standard normal distribution.