Question

A teacher administers a standardized math test to his class of 75 students. The mean score (out of 300 possible points) is 235. From previous studies, you know the population standard deviation is 28. Using the sample data given, calculate a 95% confidence interval for the population mean.

Answer 1

(228.663 ; 241.337)

Explanation:

Given that:

Mean (m) = 235

Standard deviation (s) = 28

α = 95%

Zcritical at 95% = 1.96

Sample size (n) = 75

The confidence interval of the population mean can be obtained using the relation :

Mean ± Error

Error = Zcritical * (s/sqrt(n))

Error = 1.96 * (28/sqrt(75))

Error = 1.96 * 3.2331615

Error = 6.33699654

Error = 6.337

Lower boundary = 235 - 6.337 = 228.663

Upper boundary = 235 + 6.337 = 241.337

(228.663 ; 241.337)