math order of operation

Math Order of Operation… What is it and how do we use it i math? “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 will get a wrong answer !

STRUGGLING WITH BODMAS? Get the assistance, on-going support and tutors you need to learn faster, make fewer mistakes and get the grades you deserve. Learn More.

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

Order of Operations

Do things in Brackets First

yes 6 × (5 + 3) = 6 × 8 =
48
not 6 × (5 + 3) = 30 + 3 =
33
(wrong)

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

yes 5 × 22 = 5 × 4 =
20
not 5 × 22 = 102 =
100
(wrong)

Multiply or Divide before you Add or Subtract

yes 2 + 5 × 3 = 2 + 15 =
17
not 2 + 5 × 3 = 7 × 3 =
21
(wrong)

Otherwise just go left to right

yes 30 ÷ 5 × 3 = 6 × 3 =
18
not 30 ÷ 5 × 3 = 30 ÷ 15 =
2
(wrong)

How Do I Remember It All … ? BODMAS !

B
Brackets first
O
Orders (i.e. Powers and Square Roots, etc.)
DM
Division and Multiplication (left-to-right)
AS
Addition and Subtraction (left-to-right)

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:

bodmas

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 ?

Multiplication before Addition:

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!

 

Start with: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 …

What about this example?

432

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

Start with: 432
32 = 3×3: 49
49 = 4×4×4×4×4×4×4×4×4: 262144

 

 

And finally, what about the example from the beginning?

Start with:7 + (6 × 52 + 3)
Brackets first and then “Orders”:7 + (6 × 25 + 3)
Then Multiply:7 + (150 + 3)
Then Add:7 + (153)
Brackets completed:7 + 153
Last operation is an Add:160

STRUGGLING WITH THE ORDER OF OPERATIONS? Get the assistance, on-going support and tutors you need to learn faster, make fewer mistakes and get the grades you deserve. Learn More.

Happy Learning!

 

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