Answer:
They should interview 1620 adults now.
Step-by-step explanation:
Margin of error of a confidence interval:
The margin of error of a confidence interval has the following format:
In which z is related to the confidence level, is the standard deviation of the population and n is the size of the sample.
In this question:
z wont change, neither will
We want to increase n as such the margin of error is reduced to one third.
We have that the margin of error is inversely proportional to the square root of the size of the sample, which means that for the margin of error to be reduced to one third, the sample size has to be multiplied by . So
180*9 = 1620
They should interview 1620 adults now.
