Question

29. The average price of a smartphone purchased by a random sample of 36 STAT 3309 students was​ $124. Assume the population standard deviation was​ $8.  

Find the​ 90% confidence interval for​ µ.

A.

​($122.80, $125.20)

B.

​($122.29, $125.71)

C.

​($121.81, $126.19)

D.

​($116.00, $132.00)

30. The average price of a smartphone purchased by a random sample of 36 STAT 3309 students was​ $124. Assume the population standard deviation was​ $8.  

What assumptions need to be made to construct a confidence interval for the population​ mean?

A.

The population must be normally distributed.

B.

The population is skewed left.

C.

The population mean will be in the confidence interval

D.

The population is skewed right.

Answer 1

Q.29) Given that, sample size ( n ) = 36

sample mean = $124

population standard deviation = 8

Confifence level = 90%

A 90% confidence level has 0.05 significance level and critical value is z = 1.645

90% confifence interval for the population mean is,

Answer: C) ($121.81 , $126.19)

Q.30) The average price of a smartphone purchased by a random sample of 36 STAT 3309 students was​ $124. Assume the population standard deviation was​ $8.

Therefore, assumptions need to be made to construct a confidence interval for the population​ mean is ,

The population must be normally distributed.

Answer: A)