Math Statistics Problem

I am plugging away at my math Homework and have come across a question I need help with, it seems like a simple answer but I am confused as to how to finish the problem if someone can help me it would be great then I could finish all my other math HW... thank you

Question: What is the weighted mean, median and standard deviation for years of service?

Years of service__________Number of Employees
1-5______________________5
6-10_____________________20
11-15____________________25
16-20____________________10
21-25____________________5
26-30____________________3

If someone could explain to me how to finish this problem it would be great ..not looking for an answer just the correct method to finishing the problem...again thank you (also please ignore the black line i just used that to separate the numbers correctly.

david

if you have a statistical calculator, input the mean of each interval ... 3, 8, 13, ...,.18 into a List. Then enter the frequencies 5, 20, ..., 3 into another list. Finally, use the 1-Var Stats feature ...

weighted mean = 12.926 years
median = 13 years
sample standard deviation = 6.016 years

hope that helped