How BIDMAS Can Help You Pass Numeracy Tests - dummies

How BIDMAS Can Help You Pass Numeracy Tests

By Colin Beveridge

BIDMAS stands for ‘brackets, indices, divide, multiply, add, subtract’ and tells you the order in which to do a complicated sum. (Indices, by the way, are little numbers above and to the right of a number, like this: 142. What it means is ‘times the number by itself that many times’, so 142 is 14 x 14 = 196, and 43 is 4 x 4 x 4 = 64).

Here’s how it works:

  • If your expression has any brackets in, work out the value of each of the brackets.

  • If your expression has any indices in, figure out what they are next.

  • Multiplying and dividing are just as important as each other – you work these out from left to right through the sum.

  • Lastly, you work out any adds or take aways you have left over at the end, again working from left to right.

Here’s a fairly nasty example:

((6 + 13) x 7 + 5 x 3) ÷ 22 x 100

The first thing to do is to take a deep breath.

Now, work out the sums one step at a time. First, look for brackets – there are two pairs. Work out the inner one first: 6 + 13 = 19. Easy – you can replace that bracket with the number now, to give the following:

(19 x 7 + 5 x 3) ÷ 22 x 100

Next up, do the remaining bracket, which contains 19 x 7 + 5 x 3. There aren’t any brackets or squares in there, so you do the times-and-divide step, working from left to right. The first times you come to is 19 x 7 – which you can work out to be 133. The next one is 5 x 3 = 15.

You don’t do 133 + 5 = 138 and then times that by 3. Remember BIDMAS! The adding and subtracting comes after dividing and multiplying.

The second bracket works out to be 133 + 15 = 148. So now you have 148 ÷ 22 x 100.

Now, you don’t have any brackets, so the next thing to work out is the index: 22 is the same as ‘two multiplied by itself’, which makes 2 x 2 = 4. The sum now becomes 148 ÷ 4 x 100.

You have just times and divide to do, and you do these sums from left to right: 148 ÷ 4 = 37. Then 37 x 100 = 3,700, which is your final answer. Phew!

When you see brackets, they mean ‘do this bit first’.