Posted by **Pat** on Monday, June 25, 2012 at 9:11pm.

How large a sample of U.S. adults is needed in order to estimate U with a 95% confidence interval of length 1.2 hours?

- Statistics -
**MathGuru**, Thursday, June 28, 2012 at 4:45pm
I assume this was part of your previous post:

A study was conducted in order to estimate u, the mean number of weekly hours that U.S. adults use computers at home. Suppose a random sample of 81 U.S. adults give a mean weekly computer usage time of 8.5 hours and that from prior studies , the population standard deviation is assumed to be 3.6 hours.

If so, use this formula:

Margin of error = z-value * sd/√n

With your data:

1.2 = 1.96 * 3.6/√n

Solve for n.

- Statistics -
**jas**, Monday, June 30, 2014 at 3:16pm
136

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