How BIDMAS Can Help You Pass Numeracy Tests
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’.