SOLUTION: A sample of 200 customers at a supermarket showed that 28 used a debit card to pay for their purchases. (a) Find the 95 percent confidence interval for the population proportion.

Question 1175556: A sample of 200 customers at a supermarket showed that 28 used a debit card to pay for their purchases.
(a) Find the 95 percent confidence interval for the population proportion. [2]
(b) Why is it OK to assume normality in this case? [2]
(c) What sample size would be needed to estimate the population proportion with 90 percent confidence and an error of +/- 0.03? [2

Answer by ewatrrr(24785) (Show Source): You can put this solution on YOUR website!


Hi
 n = 200, 28 used debit card
 sample p = 28/200 = .14
ME = 
95% confidence interval
ME =  = ± .0481
CI = .14 ± .0481

b) Yes, np = 28 > 5

c) n = 
 90% confidence interval
  n = = 362.006
Sample Size 362 needed.
Wish You the Best in your Studies.
 = CI	z = value
90%	z =1.645
92%	z = 1.751
95%	z = 1.96
98%	z = 2.326
99%	z = 2.576

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