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 Post subject: BIDMAS
PostPosted: Thu Oct 05, 2017 4:03 pm 
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Joined: Sat Jan 09, 2016 6:45 pm
Posts: 303
Can anyone tell me which order to complete the following when there are no brackets. Should I follow BIDMAS or does this not apply?

95-17+56-5 =

83g - 15g + 91g =

Thanks!


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 Post subject: Re: BIDMAS
PostPosted: Thu Oct 05, 2017 4:05 pm 
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Joined: Mon May 16, 2011 2:05 pm
Posts: 6886
Location: Reading
It doesn't matter if you just have addition and subtraction as you have here. Try it for yourself, you should get the same answers.


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 Post subject: Re: BIDMAS
PostPosted: Thu Oct 05, 2017 4:15 pm 
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Joined: Fri Mar 10, 2017 5:06 pm
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The BIDMAS acronym is actually a little misleading as it implies that Division comes before multiplication and addition before subtraction. That's NOT the case. The order is:

1. Brackets
2. Powers(indices)
3. Multiplication and division (both equal priority)
4. Subtraction and addition (both equal priority)

All other things being equal, work left to right.


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 Post subject: Re: BIDMAS
PostPosted: Thu Oct 05, 2017 4:21 pm 
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Joined: Mon Feb 12, 2007 2:21 pm
Posts: 16254
Surferfish wrote:
All other things being equal, work left to right.


I disagree, in the first one, for example

95-17+56-5 =

95 - 5 is the best first step if you are working it out in your head.


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 Post subject: Re: BIDMAS
PostPosted: Thu Oct 05, 2017 4:24 pm 
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Joined: Fri Mar 10, 2017 5:06 pm
Posts: 682
Tinkers wrote:
It doesn't matter if you just have addition and subtraction as you have here. Try it for yourself, you should get the same answers.


Not necessarily.

Take the OP's example.

95 - 17 + 56 - 5

Correct answer is 129.

But if you tried to follow BIDMAS literally with the 'A' before the 'S', you might work it out as:

95 - 73 - 5 = 17.


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 Post subject: Re: BIDMAS
PostPosted: Thu Oct 05, 2017 4:30 pm 
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Joined: Mon Feb 12, 2007 2:21 pm
Posts: 16254
Suterfish - that's rubbish - the signs belong to the number they are in front of.


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 Post subject: Re: BIDMAS
PostPosted: Thu Oct 05, 2017 4:34 pm 
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Joined: Fri Mar 10, 2017 5:06 pm
Posts: 682
Guest55 wrote:
Surferfish wrote:
All other things being equal, work left to right.


I disagree, in the first one, for example

95-17+56-5 =

95 - 5 is the best first step if you are working it out in your head.


Ok, I agree that if you know what you're comfortable in what you're doing you can switch some of the terms around for convenience.

The danger of this though is that they can sometimes get the +/- signs wrong and then end up with the wrong answer. (like in the example I gave)

What I meant was that with BIDMAS, logically speaking the order goes left to right if the other things are equal.


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 Post subject: Re: BIDMAS
PostPosted: Thu Oct 05, 2017 4:38 pm 
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Joined: Mon Feb 12, 2007 2:21 pm
Posts: 16254
Switching the order is taught in schools - it's basic to understand the sign belong the the number following it.

This approach starts in KS1 ..


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 Post subject: Re: BIDMAS
PostPosted: Thu Oct 05, 2017 4:44 pm 
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Joined: Fri Mar 10, 2017 5:06 pm
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Guest55 wrote:
Suterfish - that's rubbish - the signs belong to the number they are in front of.


It's obviously rubbish to you because you're an expert in maths and understand that! Plenty of children (and adults for that matter) make that mistake though when they think that addition comes before subtraction in BIDMAS, and I think that was probably the reason the OP asked the question in the first place.


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 Post subject: Re: BIDMAS
PostPosted: Thu Oct 05, 2017 4:51 pm 
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Joined: Mon Feb 12, 2007 2:21 pm
Posts: 16254
I've never met anyone like that - 6 year olds are expected to know it.


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