Question

The length of human pregnancies from conception to birth varies according to a distribution that can be modeled by a normal random variable with mean 269 days and standard deviation 17 days.

A) What percent of pregnancies last between 240 and 270 days? Note that the answer is requested as a percent. Use 2 decimal places in your answer.

B) The longest 20% of pregnancies last at least how many days? (round to the nearest whole day)

days.

Answer 1

Given that, mean (μ) = 269 days and

standard deviation = 17 days

A) We want to find, P(240 < X < 270)

Therefore, the percentage of pregnancies last between 240 and 270 days is 48.03%

B) We want to find the value of x such that, P(X > x) = 0.20

Therefore, the longest 20% of pregnancies last at least 283 days