Answer:
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:
( y = 4x/5 + 2)
m1.m2 = -1
4/5.m2 = -1
m2 = -5/4
formula = y - y1 = m2 ( x - x1)
y - 3 = -5/4 ( x - 6)
y -3 = -5x /4 + 30/4
y = -5x /4 + 21/2
C) All integers where n is greater than or equal to 1