In order to test a claim that a population mean is equal to

In order to test a claim that a population mean is equal to 21 a sample of 256 observations was drawn. The sample yielded a mean of 21.25. What is the value of the Z test statistic to test this claim, if the population standard deviation is known to be 1.6?

Solution

Test Statistic
Population Mean(U)=21
Given That X(Mean)=21.25
Standard Deviation(S.D)=1.6
Number (n)=256
we use Test Statistic (Z) = x-U/(s.d/Sqrt(n))
Zo=21.25-21/(1.6/Sqrt(256)
Zo =2.5