An educational psychologist wishes to know the mean number of words a third grader can read per minute. She wants to make an estimate at the 80% level of confidence. For a sample of 840 third graders, the mean words per minute read was 40.6. Assume a population standard deviation of 4.1. Construct the confidence interval for the mean number of words a third grader can read per minute. Round your answers to one decimal place.

The 80% confidence interval for the mean number of words a third grader can read per minute is between 40.4 wpm and 40.8 wpm.

Step-by-step explanation:

We have that to find our level, that is the subtraction of 1 by the confidence interval divided by 2. So:

Now, we have to find z in the Ztable as such z has a pvalue of .

So it is z with a pvalue of , so

Now, find M as such

In which is the standard deviation of the population and n is the size of the sample.

The lower end of the interval is the sample mean subtracted by M. So it is 40.6 - 0.2 = 40.4 words per minute.

The upper end of the interval is the sample mean added to M. So it is 40.6 + 0.2 = 40.8 words per minute.

The 80% confidence interval for the mean number of words a third grader can read per minute is between 40.4 wpm and 40.8 wpm.

step-by-step explanation:

what grade level is this? need to know so i can look in my old textbooks!