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 Post subject: Maths question-number cardsPosted: Tue Apr 29, 2014 12:31 pm

Joined: Tue Apr 29, 2014 12:07 pm
Posts: 9
Hi all
Wondered if anyone could help with the question on a past paper with 5 number cards and you need to complete a calculation

1 4 5 7 9

Use all 5 cards to complete the calculation

___ ____ _____ - _____ ______ = 654

Is there a short cut to work these out or is it just trial and error?

Thanks for any help!

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 Post subject: Re: Maths question-number cardsPosted: Tue Apr 29, 2014 1:06 pm

Joined: Mon Aug 12, 2013 9:13 am
Posts: 452
Hit n trial but the hint lies in number 54 which can be obtained by subtracting
9-5=4
9-4=5

7 9 9
1 4 5
----------
6 5 4
----------

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 Post subject: Re: Maths question-number cardsPosted: Tue Apr 29, 2014 1:14 pm

Joined: Tue Dec 18, 2012 10:59 am
Posts: 3579
parent2013 wrote:
Hit n trial but the hint lies in number 54 which can be obtained by subtracting
9-5=4
9-4=5

7 9 9
1 4 5
----------
6 5 4
----------

There are only 5 numbers!

You know you are reducing the first number by less than 100 because there is only two gaps after the minus and it has to be more than 600, so hundreds column can only be 7. Then start at units...what makes 4? 9-5 or 5-1, then look at tens, what makes 5 (1)4-9 or 9-4

So by process and a bit of trial and improvement 745 -91 =654

Edited...due to gumbiness

Last edited by southbucks3 on Tue Apr 29, 2014 2:49 pm, edited 1 time in total.

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 Post subject: Re: Maths question-number cardsPosted: Tue Apr 29, 2014 2:13 pm

Joined: Mon Aug 12, 2013 9:13 am
Posts: 452
southbucks3 wrote:
So by process 795-41 =654

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 Post subject: Re: Maths question-number cardsPosted: Tue Apr 29, 2014 2:30 pm

Joined: Tue Dec 18, 2012 10:59 am
Posts: 3579
Ok so what's a hundred between friends

We are both pants! Good job we are not ten

Same theory, but 745 -91 =654 . Which is what I had written on a til receipt, but obviously lost my brain on the iPad!

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 Post subject: Re: Maths question-number cardsPosted: Tue Apr 29, 2014 9:51 pm

Joined: Thu Apr 04, 2013 10:39 am
Posts: 654
I think the following approach may be worth mentioning as it avoids trail and error.

Let ab denote the 2 digit number and cde denote the 3 digit number and let us start by adding 654 to ab.

654
+ ab
-----
cde

There is a carry of 1 into hundreds which implies c=7.
5+b leads to a carry and 5+b is not = 10 which implies a=9
5+9=10+d which implies d=4
no carry from units column which implies b=1 and e = 5

ab is 91 and cde is 745

DS in Y6 went for the trial and error approach, though this was at 9:15PM and after 1.5 hours of swimming squad training!

nyr

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 Post subject: Re: Maths question-number cardsPosted: Thu May 01, 2014 11:01 am

Joined: Thu May 01, 2014 9:11 am
Posts: 6
Very complicated method

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