A B
01 20 10
02 5 15
02 5 15
The first row is the column label and the first column shown is the row label. Highlight Cell A1:B2. Have you ever notice that the total sum of 50 is shown near to the botton right hand corner of the spreadsheet. You don't need to enter a sum formula to find the total.
And if you have known that, then do you know that you could let the results shows the average of the 4 numbers, i.e. 12.5. How do I do that? Point your mouse at the status bar. (If you don't see the status bar, you could go to menu, view and activate the status bar option). Click on the right mouse button and you could see the list which allows you to select whether you want to see the sum (as shown above), average, etc. Select the one that you uses most often and start calculating how much time you have saved with this new discovery.