Mr F’s Maths Notes

Number

3. BODMAS / BIDMAS

3. Bidmas

A question…

What is: 3 + 2 x 4 ?

Now, if you said 20, then I am afraid you are wrong.If you try the sum on your calculator – and so long as it is not one of those you get free in a cereal packet – then the answer that should appear on the screen is 11

But why?...

Well, it’s all to do with BODMAS, or BIDMAS depending on which one you prefer.This is a set of rule which tells you which order you must do operations (like add, divide etc) in order to get questions like the one above correct.

So, what does it stand for?...

B BracketsIf there are any brackets in your sum, work out what is inside them first. And remember: you must use the rules of Bodmas inside your brackets!

O or IOrder or Indices

Next up you must look for powers, such as 23 and work them out

D DivideNow it’s time to sort out your divisions. And

remember: divisions can look like this: ÷ or this:9

4

M Multiply Next comes the multiplications

A Add Then add the additions

S Subtract And last but not least, the subtractions

And so long as you follow these rules carefully, you shouldn’t go wrong!

But let’s go through three examples together…

Example 1 – Quite Nice

20 (3 2) 3

1. The first thing we need to do is to sort those brackets out. 3 + 2 = 5, so we are left with this new sum:

20 5 3

2. We have no powers and no divisions, so next up is our multiplication. 5 x3 = 15, leaving us with this:

20 15

3. And now life is easy! 5

So, as I hope you can see, all we need to do is break down long, complicated sums into smaller, more manageable ones. And so long as we take our time, and write down each step, we should be okay.

But they do get harder…

Example 2 – A Bit Trickier

23 (2 3 3) 5 1. Again, the first thing we need to do is to sort those brackets out. Let’s concentrate on them and worry about the rest of the sum later:

2(2 3 3)

2. We must make sure we use the same rules of Bodmas inside the brackets. So first we must deal with our power. Remember: 32 is 9, not 6!

(2 9 3)

3. No divisions, so next up is the multiplication: (18 3)4. Which leaves as a nice subtraction, and tells us the value of our brackets: 155. Now we can return to our original problem, and thankfully it looks a lot nicer: 3 15 5 6. Keep your brain switched on at this point and remember to do the division first. 3 37. And even though you might have to go onto two hands to count your fingers, you should get the answer to this one correct

6

Right, are you ready for this one…

Example 3 – A Nightmare3

10 2 3

10 2

1. Now, you might not think there are any brackets on this sum… but there are! Whenever the division line goes right across, it is like there are brackets on the top and the bottom, because the whole of the top must be divided by the whole of the bottom:2. Right, let sort the top bracket out first: (10 2 3) 3. Usual deal, multiplication first:

4. Which means the top of the division is easy enough to work out:

16

5. Now we have the bottom to deal with:

6. We have to do the power first, and remember, 23 is 8, it is definitely not 6!

7. Which tells us that the bottom of the division is: 2

Phew! And if you followed that, you deserve a break!

3

(10 2 3)

(10 2 )

(10 6)

3(10 2 )

(10 8)

8. Which leaves us with a very nice division to do:16

29. Which finally gives us our answer: 8

Good luck with your revision!