Posted by Jane on Sunday, February 10, 2013 at 4:32pm.
The lengths of pregnancies are normally distributed with a mean of 273 days and a standard deviation of 20 days. If 64 women are randomly selected, find the probability that they have a mean pregnancy between 273 days and 275 days.

Statistics  MathGuru, Sunday, February 10, 2013 at 5:35pm
Use zscores:
z = (275  273)/(20/√64) = ?
Once you calculate the zscore, check a ztable from mean to that z for your probability.

Statistics  Jane, Sunday, February 10, 2013 at 6:36pm
2/2.5 = 0.8 z=0.7881 10.7881 = 0.2119
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