Question

Sat scores have a mean of 500 and a standard deviation of 100. let's contine with the above example: if we wanted a 95% confidence interval to be from 490 to 510, how big would the sample have to be

Answer 1

385

Explanation:

Given that :

Mean, m = 500

Standard deviation, s = 100

Zcritical at 95% = 1.96

Confidence interval, C2 - C1 ; 510 - 490

Using the relation :

n = (2 * Zcritical * s) / (C2 - C1)

n = sample size

n = [(2 * 1.96 * 100) / (510 - 490)]^2

n = (392 / 20)^2

n = 19.6²

n = 384.16

n = 385