BASIC MICROSOFT EXCEL FUNCTIONS 

Function:  Type this, for example (but first, click once in the cell where you want the result to go): 
Addition  =X1+X2+X3 
Subtraction  =X1X2 
Multiplication  =X1*X2 
Division  =X1/X2 
Sum  =SUM(X1:X14) 
Sheets  =Sheet1!X2 (place this formula in a cell on a different sheet. You can have more than one sheet in an Excel file.) 
Sum using Sheets  =Sheet1!X1+Sheet2!X1+Sheet3!X1 
Sum for many Sheets  =Sum('Sheet1:Sheet9'!X1) 
where X1, X2, and X3 represent, for example, the cells A1, A2, and A3 (or any other cells) 