SOLUTION: A sample of 400 racing cars showed that 80 cars cost over $700,000. What is the 99% confidence interval of the true proportion of cars costing over $700,000?

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Question 465515: A sample of 400 racing cars showed that 80 cars cost over $700,000. What is the 99% confidence interval of the true proportion of cars costing over $700,000?
Answer by edjones(8007) About Me  (Show Source):
You can put this solution on YOUR website!
p=mu=80%2F400=0.2, q=0.8, n=400
sigma=sqrt%28pq%2Fn%29=sqrt%28%28.2%2A.8%29%2F400%29=.02
(a,b)= p%2B-z%5Balpha+2%5D*sigma=.2+-(2.576*.02)=(.1485, .2515)
We can say with 99% confidence that the proportion of cars costing over $700,000 is in the interval (.1485, .2515).
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Ed