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.
I am studying for an exam and I have been stuck on this problem for a really long time. I would really appreciate it if anyone could help me solve this.
Thanks :)
I am studying for an exam and I have been stuck on this problem for a really long time. I would really appreciate it if anyone could help me solve this.
Thanks :)
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Sampling distribution of mean of 64 observations has a STD dev of 20/sqrt(64)=2.5.
convert 273 and 275 to z-scores and get probability by table lookup in normal table.
For example, 273 is (273-273)/2.5=0; 275 is (275-273)/2.5=0.8.
Now find prob of STD normal variable being between 0 and 0.8.
convert 273 and 275 to z-scores and get probability by table lookup in normal table.
For example, 273 is (273-273)/2.5=0; 275 is (275-273)/2.5=0.8.
Now find prob of STD normal variable being between 0 and 0.8.