A research firm collects a random sample of 1500 customers at a particular store. The sample shows that the average transaction for the sample was $138 with a standard deviation of $43. Calculate a 95% confidence interval for the mean.

Of those 1500 customers, 673 of them used coupons. Calculate a 95% confidence interval for the percentage of customers who used coupons when making a purchase.

## Monday, May 9, 2011

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n=1500 x=138 sd=43

ReplyDelete138+-1.96(43/1500^1/2)

138+-2.17

135.83 to 140.17 at 95% confidence

.45+-1.96(.45(1-.45) / 1500)^1/2

.45+-.0255

.425 to .475

Second part is done incorrectly. I'll fix it shortly.

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