Question

The gallup poll interviews 1600 people. of these, 18% say that they jog regularly. the news report adds: "the poll had a margin of error of plus or minus three percentage points." you can safely conclude that

a. 95% of all gallup poll samples like this one give answers within ±3% of the true population value.
b. the percent of the population who jog is certain to be between 15% and 21%.
c. 95% of the population jog between 15% and 21% of the time.
d. we can be 3% confident that the sample result is true.
e. if gallup took many samples, 95% of them would find that exactly 18% of the people in the sample jog.

Answer 1

The correct is b.

This is because, confidence interval is given by:
Confidence interval = p +/- error
In this case,
p = 18%
error = 3%

Therefore;
Confidence interval = 18+/-3 = [(18-3),(18+3)] = [15,21].
Therefore it will be true to say that the percentage of those who jog is between 15% and 21%.