Cars may be violating clean air emissions standard

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Reference no: EM13760878

An environmental agency worries that many cars may be violating clean air emissions standards. The agency hopes to check a sample of vehicles in order to estimate that percentage with a margin of error of 6% and 90% confidence. To gauge the size of the problem, the agency first picks 80 cars and finds 20 with faulty emissions systems. How many should be sampled for a full investigation?

The data set in the accompanying table contains last month's credit card purchases of 100 customers randomly chosen from a segment of a major credit card issuer. The marketing department is considering a special offer for customers who spend more than $1000 per month on their card. From these data construct a 90% confidence interval for the proportion of customers in this segment who will qualify.
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For parts a and b, use the t tables, software, or a calculator to estimate.
a) the critical value of t for a 90% confidence interval with df=27.
b) the critical value of t for a 99% confidence interval with df=88.
a) What is the critical value of t for a 90% confidence interval with df=27?
(Round to two decimal places as needed.)

For parts a and b, use the t tables, software, or a calculator to estimate.
a) the critical value of t for a 90% confidence interval with df=24.
b) the critical value of t for a 98% confidence interval with df=82.

a) What is the critical value of t for a 90% confidence interval with df=24?
(Round to two decimal places as needed.)
b) What is the critical value of t for a 98% confidence interval with df=82?
(Round to two decimal places as needed.)

Reference no: EM13760878

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