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Y5 Math homework help please?

(20 Posts)
BarkisIsWilling Wed 23-Sep-09 22:20:43

"I am thinking of two numbers, the total of which is 5000, and the difference of which is 1354, what are the numbers?"

Mumsnetters, HELP please - and in terms my 9 yo can understand.

Thanks :D

PandaG Wed 23-Sep-09 22:30:03

I'd say

2500 add 2500 = 5000

but no difference in numbers

1354/2 = 677

2500 - 677 = 1823
2500 + 677 = 3177

1823+3177 = 5000

3177-1823 = 1354


thedolly Wed 23-Sep-09 22:37:51

x + y = 5000
x - y = 1354
2x = 6354
x = 3177

3177 + y = 5000
y = 5000 - 3177
y = 1823

seems a bit of a big ask for a 9 yo

blithedance Wed 23-Sep-09 22:47:50

Total means adding up

Difference means taking away.

So one number is say mystery number X and the other is X+1354.

But we know that they add up to 5000.

so X + (X + 1354) = 5000

Take away the 1354 from the 5000

X + X = 3646

Divide that by 2

X = 1823

So the bigger number is 1823 + 1354 = 3177 as dolly said.

whippet Wed 23-Sep-09 22:47:57


DS is in Year 5, top set, and couldn't do either of the two suggested methods so far.

Do you think it could just be an extremely badly worded question asking for the difference between 5000 and 1354 i.e. 3646?

What are the other questions like? Are they all 'putting sums into words' types?

dogonpoints Wed 23-Sep-09 23:02:08

tricksy question.

I'd write a note saying your ds didn't know how to work it out and you didn't either

ZZZenAgain Wed 23-Sep-09 23:07:32

that's so clear blithe.

My dd would have been stumped.

PandaG Thu 24-Sep-09 08:04:46

just asked ds (Y5) if he could do this, and he did it exactly the same as me. first of all he said one must be bigger than 2500, and one smaller, and then could immediately see that one had to be half 1354 bigger, and one half 1354 smaller.

I just showed him how to do it algebraically too.

Madsometimes Thu 24-Sep-09 11:20:21

That seems really hard for Y5, I did not do simultaneous equations until Y9.

thedolly Thu 24-Sep-09 11:37:23

PandaG I can see the logic in your method and I could see how it would be derived from an investigation of simpler numbers first.

My brain went straight to algebra on this occasion which is a pity as there is a certain simplicity doing it your way smile.

The sum of 2 numbers is 10 and the difference is 6 for example you could do by trial and error in order to spot a pattern and then develop a method.

I suspect OP that this is the kind of activity that gave rise to the somewhat overwhelming homework.

mathanxiety Thu 24-Sep-09 16:29:47

I did it like blithedance but I can't figure out why. That's the way I learned it, but I was taught a lot of rote methods without the reasoning behind them (hence my MN name smile). PandaG's method makes a lot of sense and could be easier to explain to a 9 yo.

PandaG Thu 24-Sep-09 17:25:14

I was chatting to a secondary maths teacher friend today, and she said that as a Y5 homework she would think that a trial and error method would be what was expected, probably from an investigation of simpler numbers as you say thedolly. smile

I was just interested to see if my DS could work out what to do, as I think this is a really hard question for that age group, and much harder than the maths homework he has brought home. My method was less 'mathematical', but was how it occurred to me to do it (I'm no mathematician, got no further than GCSE but quite like maths). I felt quite thick when thedolly and blithedance so simply did the alegbra, as that hadn't occurred to me at all, but I could understand it, and try to explain it to DS.

mathanxiety, from what I have seen, maths does seem to be taught with the reasons behing why you do what you do. DS's methods seem longwinded to me, but he really understands the concepts behind them. It helps that I ask said maths teacher friend to explain how the new methods work, so I can get it too.

KittyCorncrake Thu 24-Sep-09 19:00:08

This is y5?
Perhaps my DS does need a tutor after all...

ZZZenAgain Thu 24-Sep-09 19:14:36

dd is year 4 but I'm also thinking we are going to need some help next year!

BarkisIsWilling Thu 24-Sep-09 20:36:24

Firstly, thanks to you all, especially PandaG, Thedolly and Blithedance. I really appreciate the quick response.

This was a bonus question, and they were told they did not have to do it, but I felt we should at least try.

Apparently, in class they get 30 seconds to do a slightly easier version of this type of thing to win house points.

KittyCorncrake, the children are divided into groups according to ability for numeracy and literacy in my daughter's school and I think the teacher is just testing how much he can stretch them. And their parents!

MmeProf Thu 24-Sep-09 20:45:17

x + y = 5000
x - y = 1354
2x = 6354
x = 3177

ninja Thu 24-Sep-09 20:49:40

Panda - I'm maths teacher and would do it like you.

MrsGhoulofGhostbourne Fri 25-Sep-09 09:08:32

Thinking about it, it is actually a variant of the fairly regularly occurring question eg - 'if there is a class of 30, and two more boys than girls - how many boys and how many girls' - but with bigger numbers...

BarkisIsWilling Fri 25-Sep-09 20:10:11

Can you do this for more than 2 numbers?

I wasn't a math-head in my younger days...

blithedance Fri 25-Sep-09 20:53:24

You need to know one fact for every unknown number. Then you have 3 way simultaneous equations but you can do it, things like this were the mainstay of A level maths IIRC.

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