BODMAS.. Mistake or correct?

[JellyTots2009]

My friend is at college and today learnt BODMAS. I asked her to send me an equation she had been given and her answer. I worked it out for myself and I got a different answer. Her teacher gave her a different answer too!

So this equation

3x2-4+5/2

Answers were;
-0.5
3.5 or
4.5

Which is correct and can people give their workings out please. I do think I've done it wrong but I followed the order!

www.mathsisfun.com/operation-order-bodmas.html

I understand your replies , thank you. I learned more about BODMAS today.

So you first do the multiplication and division which turns it into 6 - 4 + 2.5
The it doesn’t matter which order you do them as 6-4+2.5 will give the same answer as 6+2.5-4

I don't get this either! I got -0.5.

At the end, if you do the 4 + 2.5 first, which makes 6.5, you're left with 6 - 6.5. Which makes -0.5.

Because its not 4 its -4. The - is attached to the number following it

As its -4 you'd do
-4 +2.5 giving -1.5.
6-1.5 is 4.5

I get - 0.5 too.

Its not 4 its -4
The + or - goes with number that follows it
+6
-4
+2.5

So you end up with +6 + (-4) +2.5

Aahh - I see! Thank you.

4.5

4.5

As above.
6-4+2.5

4.5

No, sorry demented I can't see on my screen how you see that as -4 rather than 2 - 4.

Its 2 + (-4)

I get -0.5 using BODMAS

No doubt it's 4.5.

This is where BODMAS can be improperly understood: because the A comes before the S, I've seen people fall into the trap of looking at

10 - 1 + 4

and saying I need to do the addition first, so 1 + 4 to get 5. Now do the subtraction 10 - 5. This is wrong as others have explained.

In BODMAS, the DM go together and once you've done brackets and exponents, you do division and multiplication from left to right.

Similarly, the AS go together and once you've done DM, you do addition and subtraction going left to right.

Because when there is a + or - its not just on its own, its associated with the number following it
So for e.g. 2 - 4 = -2

If you wanted to do the sum in a different order to give the same answer it would be
-4 + 2 = -2

If you separated the the + and - from their number you would get the wrong answer

Addition and subtraction are of equal importance so you do them in order left to right once multiplication and division has been done

In the example given above
10 - 1 + 4 you can do addition first but it would be -1+4 giving +3 (not 1+4)
10+3 = 13

But there wasn't a + sign before the -4.
I see 2-4

Yes you don't see it but 2 means +2 and the '-' before the 4 'belongs' to the 4 and means -4
So its +2 + (-4)

How would you turn 2-4 round to give the answer -2?

4-2 is wrong so to get the same answer it would be -4 +2 as you keep the '- ' with the 4

Past weirdly I think we’ve looked at 4-2 the wrong way. Or maybe just me relearning

The - is attached to the number it precedes

It means -4

I asked dd who's currently doing GCSE maths and she explained it differently. She says it's 4.5 though. I'm still not sure why you're talking about negative numbers but I'm now happy with 4.5. :)

6-4+2.5

You can do it as is , which would be 2+2.5.
You can do it as 6+2.5-4 ,which would be 8.5-4
Or if you insist in doing the addition first,
-4 (the minus follows the number ,you can't just take the number by itself) + 2.5 which is -1.5. Then you're left with 6 - 1.5 which is also 4.5.

Basically if you do the addition first,the value isn't 4 on it's on it's -4.

Marsha it was just me trying to do DMAS in strict order. Dd says that as long as you do the DM and AS pairs in order then it will it's fine. You could do MD and SA so once you have done the MD you can work left to right rather than doing the addition before the subtraction.

Past ah I see
I did a lot of maths at university (economics) so was fine at it at school but for the life of me can’t recall BODMAS. Have been doing it with Ds though