Question

A confidence interval for the average time it takes a prospective employee to take a basic skills test is to be constructed at a 99.74% confidence. If the population deviation for the data in question is 45 minutes, and the researcher desires a margin of error of 1.9 minutes, then what should be the sample size?

Answer 1

Solution :

Given that,

standard deviation = = 45

margin of error = E = 1.9

At 99.74% confidence level the z is ,

  = 1 - 99.74% = 1 - 0.9974 = 0.0026

/ 2 = 0.0026 / 2 = 0.0013

Z_/2 = Z_0.0013 =3.011

Sample size = n = ((Z_/2 * ) / E)²

= ((3.011 *45) / 1.9)²

= 5085.34

= 5085.

Sample size = 5085