Posted by **Haywood** on Friday, July 1, 2011 at 5:22pm.

A school psychologist is trying to determine the lower boundary of a confidence interval for a IQ measure that has a mean of 100 and a standard deviation of 30 and a sample size of 100. What is the lower boundary if she was to create a 95% confidence interval?

- statistics -
**MathGuru**, Friday, July 1, 2011 at 7:39pm
CI95 = mean + or - 1.96(sd/√n)

...where + or - 1.96 represents the 95% confidence interval using a z-table, sd = standard deviation, √ = square root, and n = sample size.

With your data:

CI95 = 100 + or - 1.96(30/√100)

I'll let you take it from here.

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