Question

The length of human pregnancies from conception to birth varies according to a distribution that is approximately Normal with mean 266 days and standard deviation 16 days. What percent of pregnancies last between 240 and 270 days (roughly between 8 months and 9 months)?

Answer 1

0.5466

Explanation:

Given that the length of human pregnancies from conception to birth varies according to a distribution that is approximately Normal with mean 266 days and standard deviation 16 days.

Let X be the length of pregnancies

X is N(266,16)

To find out the probability that pregnancies last between 240 and 270 days (roughly between 8 months and 9 months)

P(240<x<270)

convert each into Z score as
`z=(x-266)/(16)`

x=240 means Z = -1.625

x=270 means z=0.25

Required prob

=
`P(-1.625<Z<0.25)\\= 0.5466`