Combined salary

There is a problem:
The following computer output comes from weekly salary information for a small company.

Gender N Min Q1 Med Q3 Max Mean STDEV

Non- graduate 10 350 500 800 900 1150 700 125

Graduate 15 400 600 1050 1300 2000 1000 250

Suppose that a graduate and non-graduate were each selected at random many times and the combined salary of the pair was computed. What would be the mean and stan. dev. of the combined salary?

Please, can you explain me what do they ask to do... I am from Russia and I have problem with understanding it... Thanks a lot !


TS Contributor
If you pick a graduate at random and a non-gaduate at random, and add their salaries together, on average the combined salaries will be the sum of the average salaries for each.

combined mean salary = mean salary(grad) + mean salary(non-grad)

For the combined standard deviation, first square each standard deviation to get the variances. Then, do the same thing as you did for the averages:

combined variance = variance(grad) + variance(non-grad)

then take the square root of the combined variance to get the combined standard deviation