Question

The lengths of pregnancies are normally distributed with a mean of 266 days and a standard deviation of 15 days. a) Find the probability of a pregnancy lasting 307 days or longer. b) If the length of pregnancy is in the lowest 44​%, then the baby is premature. Find the length that separates premature babies from those who are not premature.

Answer 1

The lengths of pregnancies are normally distributed with  

a) the probability of a pregnancy lasting 307 days or longer =

( using excel formula 1-NORM.S.DIST(2.7333,TRUE))

b) Let the length that separates premature babies from those who are not premature be A

the critical value corresponding to probability 0.44 is -0.1510 (using excel formula NORM.S.INV(0.44) )

the length that separates premature babies from those who are not premature.is 263.7 days