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Interesting P.3 Maths

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kido:
Last year I (my son in fact) encountered the following maths problem, he couldn't solved it and asked me.  It's in the photo. It's quite interesting as it's like an IQ question rather than an ordinary maths question.

It worthed quite a while(really quite some time, haha ) for me to understand what it was trying to teach me. 

Also I'm just wondering how a P3 student could solve this problem.


--- Quote ---To translate:

Given: 21 - 12 = (2-1) * 9 = 9

and 710 - 170 = (7-1) * 90 = 540

calculate

Q5. 630 - 360
Q6. 2729 - 2279


--- End quote ---

q:
630 - 360 = (6 - 3) * 90 = 270

2729 - 2279 = (7 - 2) * 90 = 450

chanchiwai:
tell me....why is it??

nobody (in school) teachs me this kind of maths before.....

pls explain...

q:
My guess is that this type of question is more about problem solving technique, and demonstrating some cool number tricks, rather than the arithmetic.

So, if we look at the examples we see:

21 - 12 = (2 - 1) * 9 = 9
710 - 170 = (7 - 1) * 90 = 540

So, the first part of the pattern is that for the flipped digits a subtraction is performed: i.e. given ab - ba then the first operation is (a - b).
The second part of the pattern is that the result of (a - b) is multiplied by 9 * 10^n where n is determined by the number of digits after ab.
So, in the trickiest case:

2729 - 2279

we would solve as:

2ab9 - 2ba9 (where a = 7, b = 2)

1 digit (the number 9) after ab so n = 1

which gives:

2ab9 - 2ba9 = (a - b) * 9 * 10^n = (7 - 2) * 90 = 450

chanchiwai:

--- Quote from: q on 09 May 2011, 09:56:13 ---My guess is that this type of question is more about problem solving technique, and demonstrating some cool number tricks, rather than the arithmetic.

So, if we look at the examples we see:

21 - 12 = (2 - 1) * 9 = 9
710 - 170 = (7 - 1) * 90 = 540

So, the first part of the pattern is that for the flipped digits a subtraction is performed: i.e. given ab - ba then the first operation is (a - b).
The second part of the pattern is that the result of (a - b) is multiplied by 9 * 10^n where n is determined by the number of digits after ab.
So, in the trickiest case:

2729 - 2279

we would solve as:

2ab9 - 2ba9 (where a = 7, b = 2)

1 digit (the number 9) after ab so n = 1

which gives:

2ab9 - 2ba9 = (a - b) * 9 * 10^n = (7 - 2) * 90 = 450



--- End quote ---

so this is a kind of primary 3 level maths?????

what a wonderful world...

I wonder this is a superhero primary 3 level.....not for my son....sorry...

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