In: Statistics and Probability
7. A political group randomly samples 60 potential voters to gauge the proportion of voters who favor a certain legislative issue. Assume the true proportion of voters who favor the issue is 75%. Find the probability that the sample fraction who favor the legislation will be within 0.10 of the true fraction.
Solution:
Given:
Sample size = n = 60
The true proportion of voters who favor the issue is 75%.
Thus p = 0.75
We have to find the probability that the sample fraction who favor the legislation will be within 0.10 of the true fraction.
That is find:
Look in z table for z = 1.7 and 0.09 as well as for z = -1.7 and 0.09 and find corresponding area.
P( Z< -1.79) = 0.0367
and
P(Z < 1.79 ) = 0.9633
thus
The probability that the sample fraction who favor the legislation will be within 0.10 of the true fraction 0.9266