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Posted by **jabrony** on Monday, November 28, 2011 at 1:31pm.

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Ten different families are tested for the number of gallons of water per day they use before and after viewing a conservation video. Construct a 90% confidence interval for the mean of the differences.

- statistics -
**PsyDAG**, Tuesday, November 29, 2011 at 11:57amSubtract before values from after values.

Find the mean = sum of scores/number of scores

Subtract each of the scores from the mean and square each difference. Find the sum of these squares. Divide that by the number of scores to get variance.

Standard deviation = square root of variance

90% = mean ± 1.645 SD

I'll let you do the calculations.

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