Verified answer

there could be a few ways to write it depending on which formula.

it always starts with =

then it could be some specific funcion, such as sum or avg

so it would be =sum

then you have the range of cells, for example a1-a3

so it would be =sum(a1:a3)

or you could even write it like =(a1+a2+a3)

You need to learn what the functions are or how to write complex formulas if you want to use much more than that.

To write formulas you need to learn how to use excel. Check these tutorials:

EXCEL 2007/2010 http://www.baycongroup.com/el0.htm

EXCEL 2003: http://www.baycongroup.com/excel2003/excel01.htm

To troubleshoot a formula you use the Formula Auditing Tools :

EXCEL 2007/2010: Within Excel, click the cell you want to evaluate. On the Formulas tab, in the Formula Auditing group, click Evaluate Formula. Click the Evaluate option to watch as Excel evaluates each step of the formula.

http://www.mrexcel.com/tip121.shtml

http://www.dummies.com/how-to/content/evaluating-a...

Auditing tools option: http://www.dummies.com/how-to/content/understandin...

Tracking formulas: http://www.mrexcel.com/tip147.shtml

Your question is like how do you fly an aeroplane...anyway you need to acquire some kind of knowledge in excel and maths..