We can either define sample mean as an estimate of the population mean or the average of all the measurements in the sample.
How to calculate sample mean.
An employer wanted to find out the mean age of his employees. Out of his 10 employees, he took the ages of 4 employees. Their ages were 21 years, 24 years, 26 years and 28 years. What is the sample mean age of the employees?
Therefore, the sample mean age is 24.75 years.