Many, many years ago a "vote" was taken on how to evaluate an arithmetic expression like the following:

3 + 4 X 5

(A) You should start on the left and get 7 and multiply that by 5 to get 35 or (B) You should multiply 4 by 5 and get 20 and add 3 to 20 to get 23. Clearly, the expression should have only one solution, but which one???

If you use a $2 calculator, you will probably get 35 since most simple calculators perform arithmetic as it is entered. If you have a scientific calculator you will get 23. Scientific calculators know about the "vote"...they know about...

The Order of Operations

When an expression has more than one operation, the proper way to evaluate the solution is to multiply and divide first and then come back and add or subtract. If you should have a few exponents in the expression, they are computed before any multiplication or division.

In the example above, you could use parentheses to indicate you wish the 3 and 4 added first. The problem would look like this:

(3 + 4) X 5

This would suggest the 3 and 4 should be added and then multiplied by 5.

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Q: Why should you keep up with this?

A: Since most people don't do much arithmetic, most people don't have a reason to remember the Order of Operations. The "cheap" response might be...If you don't know about the Order of Operations, you probably won't be entering many formulas into an Excel project!

For those who might use a little more arithmetic than others, consider these two examples:

Problem	Incorrect	Correct
3 + 7 ----- 4	3 + 7 / 4	(3 + 7)/4
6 - 5 ----- 8 + 4	(6-5)/8 + 4	(6-5)/(8 + 4)

Comments:

Excel would evaluate 3 + 7/4 using the Order of Operations. (Would you expect Excel to calculate like a $2 calculator?) That is, it will first compute 7/4 and add 3. The correct version directs Excel to add the 3 and 7 then to divide the sum by 4

Excel will evaluate (6-5)/8 first and get 1/8. Then 4 would be added. Wrong! The correct version would subtract 5 from 6, add 8 to 4, and then compute 1/12.

Moral of the Story - Don't forget about The Order of Operation if you have a formula which has more than one operation....Excel won't forget!

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