When a woman learns she is pregnant, her doctor usually calculates a “due date”

Question

When a woman learns she is pregnant, her doctor usually calculates a “due date” for the baby. The due date represents the date on which the baby will be born if her pregnancy lasts the mean length for all pregnancies. Actual lengths of pregnancy terms turn out to be nearly normally distributed about this due date (the mean) with a standard deviation of 15 days.

a. About what percentage of births occur within 15 days of the due date?

b. About what percentage of births occur within 1 month of the due date?

c. About what percentage of births occur more than 15 days before the due date? Based on your answer, do you think it is a good idea for a pregnant woman to fly to an important meeting 15 days before the due date? Explain.

Explanation / Answer

standard deviation = 15 days

As we know from the 68-95-99.7 rule

68.27%, 95.45% and 99.73% of the values lie within one, two and three standard deviations of the mean

a) Hence within 15 days i.e within 1 standard deviation 68.27(68)% of birth will occur.

b)within 1 month(30 days) i.e within 2 standard deviation 95.45(95)% of birth will occur.

c)

As 68.27 % of bith occur within 15 days of the mean and it being normally distributed we can say that 34.135(34%) % of birth will occur from from mean date to 15 days before the mean date.

Also as 50% of births will occur before the mean date we can say that

(50 - 34.135) % of births occur more than 15 days before the due date.

i.e 15.865 (16) %

Here percentages in bracket are in more simplied percentages.

Related Questions

Navigate

• Browse (All)
• Browse W
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.