Question

In order to estimate the population proportion of Texas voters who support a state sales tax for public schools to within 5% with 95% confidence, the sample size should be:

A. 271

B. 384

C. 385

D. None of the above

Answer 1

Solution :

Given that,

= 0.5

1 - = 1 - 0.5 = 0.5

margin of error = E = 5% = 0.05

At 95% confidence level the z is ,

= 1 - 95% = 1 - 0.95 = 0.05

/ 2 = 0.05 / 2 = 0.025

Z/2 = Z0.025 = 1.96 ( Using z table )

Sample size = n = (Z/2 / E)2 * * (1 - )

= (1.96 / 0.05)2 * 0.5 * 0.5

= 384.16

Sample size =384 ROUNDED