The BIDMAS rule

There is an agreed order of operations in Maths called BIDMAS.

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BIDMAS stands for Brackets, Indices, Division and Multiplication, Addition and Subtraction.

All of these terms are fairly obvious except for 'Indices' - which are just powers, eg 2^3 or 4^2.

'Indices' are also known as 'orders', which gives us the term BODMAS (Brackets, Orders, Division and Multiplication, Addition and Subtraction).

So the order you should do your calculations in is:

  • Brackets
  • Indices
  • Division and Multiplication (start on the left and work them out in the order that you find them)
  • Addition and Subtraction (when only addition and subtraction are left in the sum, work them out in the order you find them - starting from the left of the sum and working towards the right)

Example 1

What is 4 + 2 \times 3?

If you calculate the 4 + 2 part first you get:

4 + 2 \times 3 = 6 \times 3 = 18

If you calculate the 2 \times 3 part first you get:

4 + 2 \times 3 = 4 + 6 = 10

These are two very different answers, but only one is correct.

In BIDMAS, multiplication comes before addition, so multiply {2} by {3} first:

4 + 2 \times 3 = 4 + 6 = 10, so this is the right answer.

Example 2

What is 9 - 4 + 3?

This sum has only addition and subtraction. So work them out from left to right:

9 - 4 + 3 = 5 + 3 = 8

Notice that if you didn't go from left to right you would get a different answer:

9 - 4 + 3 = 9 - 7 = 2

That would be incorrect, which is why we work them out from left to right.