What is the mean for 20 30 40 50 60 70 80 90 110 120 130?

TO find the mean of a group of numbers you simply find the average. To do that, just simply add up all the numbers, then divide by how many numbers there are. So when you add up all of those numbers you get to a sum of: 800
Then divide by the totaly amount of numbers which is 11, so 800 divided by 11 equals: 
The mean for those set of numbers is: 72.7272 reapeating so...
72.72 (with a little line over the digits on the right side of the decimal)