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 Post subject: Maths question help pleasePosted: Tue Jun 09, 2015 12:08 pm

Joined: Thu Nov 27, 2014 4:04 pm
Posts: 1125
Hi all

Can I just check a couple of things that my ds (end of year 5) is doing for maths homework - I know how to do the questions but want to make sure I'm giving the right advice.

He was doing questions yesterday that were like this

2a + 20 / 4 = 9

So the 2a + 20 was all over the same denominator ie 4. I told him that if a sum is over the same denominator then he should write it in brackets. Is that right? It wasn't in brackets so he was trying to do 2a/4 + 20/4 which doesn't give the same answer. He is doing BODMAS at school at the moment (I know I have read on here that they shouldn't be doing that in year 5 but he is so I am just trying to make sure he does it right). I know I assume that I treat it as though it's in brackets.

The other thing is that if we take another question

a/5 -11 = 44

he is just doing it all in his head and when I ask why he is doing what he is doing, he doesn't really know. He just says it's obvious. But I am trying to explain to him that things may seem intuitive when they are relatively simple numbers but they will be problematic when the numbers are more complex. I have tried to explain it with scales on either side of the = sign etc. Should I be insisting that he shows how he is working something out or is it ok at this stage just to do it without any real understanding?

Thanks for any help.

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 Post subject: Re: Maths question help pleasePosted: Tue Jun 09, 2015 12:20 pm

Joined: Mon Feb 12, 2007 1:21 pm
Posts: 14005
Quote:
He was doing questions yesterday that were like this

2a + 20 / 4 = 9

So the 2a + 20 was all over the same denominator ie 4. I told him that if a sum is over the same denominator then he should write it in brackets. Is that right? It wasn't in brackets so he was trying to do 2a/4 + 20/4 which doesn't give the same answer. He is doing BODMAS at school at the moment (I know I have read on here that they shouldn't be doing that in year 5 but he is so I am just trying to make sure he does it right). I know I assume that I treat it as though it's in brackets.

I'm confused - brackets aren't needed and you should get the same answer if you write 2a/4 + 20/4 as it is the same!

I would use scales and talk about inverse operations - needing to multiply both sides of the equation by 4.

Quote:
The other thing is that if we take another question

a/5 -11 = 44

he is just doing it all in his head and when I ask why he is doing what he is doing, he doesn't really know. He just says it's obvious. But I am trying to explain to him that things may seem intuitive when they are relatively simple numbers but they will be problematic when the numbers are more complex. I have tried to explain it with scales on either side of the = sign etc. Should I be insisting that he shows how he is working something out or is it ok at this stage just to do it without any real understanding?

The problem with equations is most they get can be guessed as the solution is a whole number so they aren't really understanding. In Year 7 this is a common issue, give them an equation with a negative or fraction as a solution and they are stuck as you mention 'numbers are more complex'.

Use scales again and insist he writes down the steps.

a/5 - 11 = 44

+ 11 to both sides

a/5 - 11 + 11 = 44 + 11

a/5 = 55 (you should line up equals signs but that's hard on here)

x 5,

a/5 x 5 = 55 x 5

a = 275 [check in original equation]

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 Post subject: Re: Maths question help pleasePosted: Tue Jun 09, 2015 12:39 pm

Joined: Thu Nov 27, 2014 4:04 pm
Posts: 1125
Thank you.

Yes it is the same! (You'd never guess I did maths A level back in the day )

OK so I can be quiet with him about that one. That's exactly how I was trying to show him how to do it because that's how dd (year 7) is being shown it. He didn't want to listen because it takes longer to write it all down. But I'll make him do it!

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