Answer:


And the best option would be:
D. (0.191 to 0.249)
Step-by-step explanation:
For this case we know that the mean is:

And the standard error is given by:

We want to construct a 68% confidence interval so then the significance level would be :
and
. The confidence interval is given by:

Now we can find the critical value using the normal standard distribution and we got looking for a quantile who accumulate 0.16 of the area on each tail and we got:

And replacing we got:


And the best option would be:
D. (0.191 to 0.249)
Answer:
The sale this month = 79
Step-by-step explanation:
Let the amount he needs to sell this month = x


Note that number of entries = number of months = 5
To maintain an average sales of 77, the amount of sale in month 5 is determined as follows:
