A simple random sample of 400 households is taken in a large city, and the number of cars in each sampled household is noted. The average number of cars in the sampled households is 1.8 and the SD is 1.3. Among the sampled households, 10% had no car.

An approximate 99% confidence interval for the percent of city households that have no car goes from _____________________% to ______________________%.

Question

A simple random sample of 400 households is taken in a large city, and the number of cars in each sampled household is noted. The average number of cars in the sampled households is 1.8 and the SD is 1.3. Among the sampled households, 10% had no car.

An approximate 99% confidence interval for the percent of city households that have no car goes from _____________________% to ______________________%.

anonymous · Answer

I don't understand what the question is asking. 10% had no car ==> 400*.1 = 40 households had no car right? Is there a formula in the book (or examples) that you can use?

anonymous · Answer

The question is about what percentage from the total population do we think will not have a car.  We know that 40 / 400 don't have a car, but what can we learn about the total population from that fact?