6) An economist is interested in studying the average income ofconsumers in a particular country. The population standarddeviation of incomes is known to be $1,000.
What type of confidence interval should the economist build?
Group of answer choices
A t-based interval for the population mean.
No answer text provided.
A Z-based interval for the population proportion.
A Z-based interval for the population mean.
7) A race car driver tested his car for the time it takes to gofrom 0 to 60 mph, and for 20 tests obtained a mean of 4.85 secondswith a standard deviation of 1.47 seconds. These times are known tobe normally distributed.
What is the value of t used to construct a 95% confidenceinterval for the mean time it takes the car to go from 0 to 60?Round your answer to 2 decimal places.
8) A quality control engineer is interested in the mean lengthof sheet insulation being cut automatically by machine. The desiredmean length of the insulation is 12 feet.A sample of 70 cut sheetsyields a mean length of 12.14 feet and a sample standard deviationof 0.15 feet.
What type of confidence interval should the engineer build?
Group of answer choices
A Z-based interval for the population proportion.
A Z-based interval for the population mean.
A t-based interval for the population mean.
