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#1 2012-12-21 06:15:13

jacks
Member
Registered: 2012-11-21
Posts: 80

4 digit no.

A 4 digit no. abcd is such that 4 *(abcd) = (dcba). Then no. abcd is

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#2 2012-12-21 06:33:17

anonimnystefy
Real Member
From: The Foundation
Registered: 2011-05-23
Posts: 15,608

Re: 4 digit no.

I have that abcd=2178.


“Here lies the reader who will never open this book. He is forever dead.

“Taking a new step, uttering a new word, is what people fear most.” ― Fyodor Dostoyevsky, Crime and Punishment

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#3 2012-12-21 06:48:18

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 89,048

Re: 4 digit no.

Hi;

Yes, and that is the only solution.


In mathematics, you don't understand things. You just get used to them.

I agree with you regarding the satisfaction and importance of actually computing some numbers. I can't tell you how often I see time and money wasted because someone didn't bother to run the numbers.

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#4 2012-12-21 07:11:18

jacks
Member
Registered: 2012-11-21
Posts: 80

Re: 4 digit no.

Yes 2178 is right answer.

How can i get it.

would you like to explain me

hanks

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#5 2012-12-21 07:20:41

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 89,048

Re: 4 digit no.

Hi;

First thing that jumps right out at you is that the front digit is either a 1 or 2. So, the last digit is a 4 or an 8. You now only have to try 16 numbers to find all the answers.


In mathematics, you don't understand things. You just get used to them.

I agree with you regarding the satisfaction and importance of actually computing some numbers. I can't tell you how often I see time and money wasted because someone didn't bother to run the numbers.

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#6 2012-12-21 22:53:52

phrontister
Real Member
From: The Land of Tomorrow
Registered: 2009-07-12
Posts: 3,854

Re: 4 digit no.

Hi,

a = 2...from d x 4 = even, and a x 4 must be a single-digit result (to avoid a 5-digit end product).
b = 1...from b x 4 must be a single-digit result (to keep a = 2), and 2 is already taken.
d = 8...from a x 4 = 8.
c = 7...from (c x 4) + the tens unit (3) from d x 4 must end in 1, which is only possible with c = 7 or 2; but 2 is already taken.

So, abcd is 2178.


"The good news about computers is that they do what you tell them to do. The bad news is that they do what you tell them to do." - Ted Nelson

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#7 2012-12-23 03:06:37

jacks
Member
Registered: 2012-11-21
Posts: 80

Re: 4 digit no.

Thanks friends got it

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