Order of Operations
BODMAS
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
4 × (5 + 3) | = | 4 × 8 | = | 32 | |||
4 × (5 + 3) | = | 20 + 3 | = | 23 | (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
A practical example:
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 |
So 432 = 4(32), not (43)2
And finally, what about the example from the beginning?
an Add
Or we could use;
Order of Operations
PEMDAS
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 Parentheses First
4 × (5 + 3) | = | 4 × 8 | = | 32 | |||
4 × (5 + 3) | = | 20 + 3 | = | 23 | (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 ... ? PEMDAS !
P | Parentheses first |
E | Exponents (ie Powers and Square Roots, etc.) |
MD | Multiplication and Division (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 "P" and "E", just go from left to right doing any "M" or "D" as you find them.
Then go from left to right doing any "A" or "S" as you find them.
You can remember by saying "Please Excuse My Dear Aunt Sally". | |
Or ... | Pudgy Elves May Demand A Snack Popcorn Every Monday Donuts Always Sunday Please Eat Mom's Delicious Apple Strudels People Everywhere Made Decisions About Sums |
Note: in the UK they say BODMAS (Brackets,Orders,Divide,Multiply,Add,Subtract), and in Canada they say BEDMAS (Brackets,Exponents,Divide,Multiply,Add,Subtract). It all means the same thing! It doesn't matter how you remember it, just so long as you get it right.
Examples
A practical example:
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 |
So 432 = 4(32), not (43)2
And finally, what about the example from the beginning?
:160
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