Posted by **jr** on Monday, October 29, 2012 at 4:01pm.

A researcher is interested in estimating the average salary of teachers in a large urban school district. She wants to be 95% confident that her estimate is correct. If the standard deviation is $1050 (σ = 1050), how large of a sample is needed to be accurate within $200 (E = 200)? That is, find n.

- statistics -
**MathGuru**, Tuesday, October 30, 2012 at 6:25pm
Formula:

n = [(z-value * sd)/E]^2

...where n = sample size, z-value will be 1.96 using a z-table to represent the 95% confidence interval, sd = 1050, E = 200, ^2 means squared, and * means to multiply.

Plug the values into the formula and calculate the sample size. Round your answer to the next highest whole number.

I hope this will help get you started.

- statistics -
**Anonymous**, Thursday, November 21, 2013 at 6:51am
105.88

- statistics -
**Jack**, Friday, October 24, 2014 at 6:18pm
105.88

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