# Bodmas rule

## Operations

“Operations” mean things like add, subtract, multiply, divide, squaring, etc. If it isn’t a number it is probably an operation.

But, when you see something like…

7 + (6 × 52 + 3)

… what part should you calculate first?

Start at the left and go to the right?

Or go from right to left?

Warning: Calculate them in the wrong order, and you can get a wrong answer !

So, long ago people agreed to follow rules when doing calculations, and they are:

## Order of Operations

Do things in Brackets First

Exponents (Powers, Roots) before Multiply, Divide, Add or Subtract

Multiply or Divide before you Add or Subtract

Otherwise just go left to right

## How Do I Remember It All … ? BODMAS !

Divide and Multiply rank equally (and go left to right).

Add and Subtract rank equally (and go left to right)

So do it this way:

After you have done “B” and “O”, just go from left to right doing any “D” or “M” as you find them.

Then go from left to right doing any “A” or “S” as you find them.

Note: the only strange name is “Orders”. “Exponents” is used in Canada, and so you might prefer “BEDMAS”. There is also “Indices” which makes it “BIDMAS”. In the US they say “Parentheses” instead of Brackets, so it is “PEMDAS”

## Examples

### Example: How do you work out 3 + 6 × 2 ?

First 6 × 2 = 12, then 3 + 12 = 15

### Example: How do you work out (3 + 6) × 2 ?

Brackets first:

First (3 + 6) = 9, then 9 × 2 = 18

### Example: How do you work out 12 / 6 × 3 / 2 ?

Multiplication and Division rank equally, so just go left to right:

First 12 / 6 = 2, then 2 × 3 = 6, then 6 / 2 = 3

A practical example:

### Example: Sam threw a ball straight up at 20 meters per second, how far did it go in 2 seconds?

Sam uses this special formula that includes gravity:

height = velocity × time − (1/2) × 9.8 × time2

Sam puts in the velocity of 20 meters per second and time of 2 seconds:

height = 20 × 2 − (1/2) × 9.8 × 22

Now for the calculations!

20 × 2 − (1/2) × 9.8 × 22

Brackets first:

20 × 2 − 0.5 × 9.8 × 22

Then Orders (22=4):

20 × 2 − 0.5 × 9.8 × 4

Then the Multiplies:

40 − 19.6

Subtract and DONE !

20.4

The ball reaches 20.4 meters after 2 seconds

## Exponents of Exponents …

432

Exponents are special: they go top-down (do the exponent at the top first). So we calculate this way:

So 432 = 4(32), not (43)2

And finally, what about the example from the beginning?

7 + (6 × 52 + 3)

Brackets first and then “Orders”:

7 + (6 × 25 + 3)

Then Multiply:

7 + (150 + 3)