Ever need to temporarily see what a grouping of numbers in an excel sheet is? Do you a) create a sum function in a new cell to see what the total of the group is or b) do you open your onscreen calculator or grab the manual one beside your stapler to punch in the numbers?
If you do a) or b) then consider c) as an option: Left click your mouse and drag it so all the numbers in the column or group are highlighted. While still highlighted, look along the bottom right of the Excel screen for the word 'SUM' and you will see the answer given.
