Question

An online used car company sells second-hand cars. For 30 randomly selected transactions, the mean price is 2000 dollars.

Part a) Assuming a population standard deviation transaction prices of 190 dollars, obtain a 99% confidence interval for the mean price of all transactions. Please carry at least three decimal places in intermediate steps. Give your final answer to the nearest two decimal places.

Confidence interval: (. , )

For each situation, state the null and alternative hypotheses: (Type "mu" for the symbol ?μ , e.g.  mu >> 1 for the mean is greater than 1, mu << 1 for the mean is less than 1, mu not = 1 for the mean is not equal to 1. Please do not include units such as "mm" or "$" in your answer.)

(a) The diameter of a spindle in a small motor is supposed to be 4.5 millimeters (mm) with a standard deviation of 0.1 mm. If the spindle is either too small or too large, the motor will not work properly. The manufacturer measures the diameter in a sample of 9 spindles to determine whether the mean diameter has moved away from the required measurement. Suppose the sample has an average diameter of 4.6 mm.
?0 :  
??:

(b) Harry thinks that prices in Caldwell are higher than the rest of the country. He reads that the nationwide average price of a certain brand of laundry detergent is $23.05 with standard deviation $1.79. He takes a sample from 4 local Caldwell stores and finds the average price for this same brand of detergent is $20.25.
?0 :
?? :

Answer 1