In a random sample of 40 refrigerators, the mean repair cost was $150. Assume the population standard deviation is $15.50. Construct a 99% confidence interval for the population mean repair cost. Then change the sample size to n = 60. Which confidence interval has the better estimate?

 ($143.69, $156.31)

Step-by-step explanation:

Confidence interval to estimate  population mean :

, where = population standard deviation

n= sample size

Sample mean

z= critical value.

As per given,

n= 40

= $15.50

$150

Critical value for 99% confidence level = 2.576

Then, 99% confidence interval for the population mean:

Hence, the required confidence interval : ($143.69, $156.31)

42.4

step-by-step explanation:

convert to decimal

explanation:

remove parenthesis:

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apply rule

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multiply fractions:

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divide:

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mordancy.