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
 | 6 × (5 + 3) | = | 6 × 8 | = | 48 | ||
 | 6 × (5 + 3) | = | 30 + 3 | = | 33 | (wrong) |
Exponents (Powers, Roots) before Multiply, Divide, Add or Subtract
| 5 × 22 | = | 5 × 4 | = | 20 | ||
| 5 × 22 | = | 102 | = | 100 | (wrong) |
Multiply or Divide before you Add or Subtract
| 2 + 5 × 3 | = | 2 + 15 | = | 17 | ||
| 2 + 5 × 3 | = | 7 × 3 | = | 21 | (wrong) |
Otherwise just go left to right
| 30 ÷ 5 × 3 | = | 6 × 3 | = | 18 | ||
| 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:
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 × 22Brackets first:20 × 2 − 0.5 × 9.8 × 22Then Orders (22=4):20 × 2 − 0.5 × 9.8 × 4Then the Multiplies:40 − 19.6Subtract 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 + 153Last 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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