SOLUTION: an electricity company estimates that 60% of its customers pay their electricity bills within 15 days of delivery. a random sample of 400 bills indicated that 180 were paid within

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Question 984258: an electricity company estimates that 60% of its customers pay their electricity bills within 15 days of delivery. a random sample of 400 bills indicated that 180 were paid within 15 days of delivery. at 0.10 level of significance is there evidence that the company's estimate is correct?
Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
p=180%2F400=0.45
SE=sqrt%28%28p%281-p%29%29%2FN%29=sqrt%28%280.45%29%280.55%29%29%2F400%29=0.02487
1.645%2A.02487=0.041
So the 90% confidence interval would be,
0.409%3Cp%3C0.491
This is nowhere near the 60% the electric company estimates so evidence exists to reject the claim.