Question

QUESTION 9

1. In a survey of 1000 people, 700 people said that they voted in the last presidential election. Let p denote the proportion of all people who voted. Find a point estimate for p and also construct a 90% confidence interval for p.

Answer 1

Solution :

Given that,

Point estimate = sample proportion = = x / n = 700 / 1000 = 0.7

1 - = 1 - 0.7 = 0.3

Z/2 = Z0.05 = 1.645

Margin of error = E = Z / 2 * (( * (1 - )) / n)

= 1.645 (((0.7 * 0.3) / 1000)

= 0.024

A 90% confidence interval for population proportion p is ,

± E

0.7 ± 0.024

(0.676 , 0.724)