Question

4. A research company conducts an opinion poll to determine what fraction of the country has a favorable opinion of the President. They randomly select 400 voters, and ask them whether they approve of the President’s performance in office. The true proportion of people who approve of the President’s performance is 42.3%. Find the probability that 42.75% of the people in the sample approve of the President’s performance.

b. What is the probability that 40% of people in the sample say they approve of the President’s performance in office?

c. Use the =BINOM.INV or =NORM.INV function to find a range that contains 95% of the sample proportions.

Answer 1

4) The sample proportion is approximately normally distributed with . Here .

a)Using continuity correction,

b)Using continuity correction,

c) A range that contains 95% of the sample proportions is ()

The above values can also be found using the EXCEL function, NORM.INV.

Syntax. NORM.INV(probability,mean,standard_dev).