What is the minimum number of days required to see 80% of pregnancies completed?

Question

Data analysis. Additional info for Question>>>>The length of human pregnancies from conception to birth is a mean 266 days standard deviation of 16 days. Multiple choices answers provided are: a-266, b-276, c-280, d-282, e-292.

Answer 1

Dear Adam,

The Normal distribution should work for modeling the length of human pregnancies. Since this distribution is symmetric about the mean, you should see 50% of pregnancies completed in 266 days (which also means that choice (a) is obviously not correct). To determine which of the remaining choices is best, you have to know a bit more about the Normal distribution, and having statistical tables or a calculator is helpful.

Recall that about 68% of outcomes will fall within one standard deviation of the mean when using the Normal distribution (i.e., between one standard deviation below the mean to one standard deviation above the mean). This implies that at the mean plus one standard deviation (266+16=282 days), we would expect to see about 84% of pregnancies completed. With this information we can definitely eliminate choice (e). We also know that choice (d) is doubtful (we know it isn't precisely correct, but would like to determine if there is another choice that is closer to the 80% figure of interest).

A quick linear interpolation here between 266 and 282 days, using 50% and 84% respectively, yields approximate values of 71.25% in 276 days and 79.75% in 280 days. Thus choice (c) appears to be closest to correct, even by using this rudimentary approximation. If you went to the effort of obtaining more precise values, you would find that 80% of pregnancies would be completed in 279.47 days, and that 80.92% of pregnancies would be completed in 280 days.

Bottom line:
The best choice is (c) 280 days.

Answer 2

if pregnancy period is 266 than 80% would be:-212 day and 19 hours 12 min
considering the deviation of 16 pregnancy period would be 250 or 282 for which 80% would be:-200 days or 225 days 14 hours 24 minutes.

Answer 3

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