In what range would you expect to find the middle 68% of most pregnancies?

Question

The lengths of pregnancies in a small rural village are normally distributed with a mean of 260 days and a standard deviation of 15 days.

In what range would you expect to find the middle 68% of most pregnancies?

If you were to draw samples of size 42 from this population, in what range would you expect to find the middle 68% of most averages for the lengths of pregnancies in the sample?

Enter your answers as numbers. Your answers should be accurate to 1 decimal places.

Answer 1

middle 68% is between 16th and 84th percentiles. The z-score for 84th percentile is approximately 1.

mean is given as 260 and standard deviation is given 15

The middle length would lie between mean +/- z-score * standard deviation

The middle average length would lie between mean +/- z-score * standard deviation/square root(sample size), where sample size is given as 42.