A sample of 255 observations is selected from a normal population with a population standard deviation of 27. The sample mean is 20. Determine the standard error of the mean.

1.691

Step-by-step explanation:

Standard error of the mean is expressed as SEM = S/√n

S is the population standard deviation

n is the sample size (number of observation)

Given S = 27 and n = 255

SEM = 27/√255

SEM = 27/15.97

SEM = 1.691

Hence the standard error of the mean is 1.691

1/4 because there is 4 grades.