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Maths question-number cards
Posted: Tue Apr 29, 2014 1:31 pm
by Mumstheword
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!
Re: Maths question-number cards
Posted: Tue Apr 29, 2014 2:06 pm
by parent2013
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
----------
Re: Maths question-number cards
Posted: Tue Apr 29, 2014 2:14 pm
by southbucks3
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
Re: Maths question-number cards
Posted: Tue Apr 29, 2014 3:13 pm
by parent2013
southbucks3 wrote: So by process 795-41 =654
Check your process again
Re: Maths question-number cards
Posted: Tue Apr 29, 2014 3:30 pm
by southbucks3
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!
Re: Maths question-number cards
Posted: Tue Apr 29, 2014 10:51 pm
by nyr
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
Re: Maths question-number cards
Posted: Thu May 01, 2014 12:01 pm
by Sutty961
Very complicated method