Answer:
The 95% confidence interval for the percent of all coffee drinkers who would say they are addicted to coffee is between 21% and 31%.
Step-by-step explanation:
In a sample with a number n of people surveyed with a probability of a success of
, and a confidence level of
, we have the following confidence interval of proportions.

In which
z is the zscore that has a pvalue of
.
The margin of error is:

A confidence interval has two bounds, the lower and the upper
Lower bound:

Upper bound:

In this problem, we have that:

Lower bound:

Upper bound:

The 95% confidence interval for the percent of all coffee drinkers who would say they are addicted to coffee is between 21% and 31%.
1: multiple both sides by 2
Ex:-7n+10=-32
2: subtract 10 from both sides
Ex: -7n=-42
3:divide both sides by -7 to get n alone
Ex: n=6
Answer is 6 and the process is elimination!
(n+20)*2 = 99.2
distribute
2n + 40 = 99.2
subtract 40 from each side
2n = 59.2
divide each side by 2
n = 29.6