Posted by **Katty** on Monday, October 3, 2011 at 1:50am.

Assume that a population is normally distributed with a mean of 100 and a standard deviation of 15. Would it be unusual for the mean of a sample of 3 to be 115 or more? Why or why not?

- Math -
**PsyDAG**, Monday, October 3, 2011 at 1:17pm
What do you mean by unusual? P < .10? P < .05? P < .01?

Z = (mean1 - mean2)/standard error (SE) of difference between means

SEdiff = √(SEmean1^2 + SEmean2^2)

SEm = SD/√(n-1)

If only one SD is provided, you can use just that to determine SEdiff.

Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion for that Z score.

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