Discussion about math, puzzles, games and fun.   Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫ • π ƒ -¹ ² ³ °

You are not logged in.

## #1 2012-12-22 05:15:13

jacks
Full Member

Offline

### 4 digit no.

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

## #2 2012-12-22 05:33:17

anonimnystefy
Real Member

Offline

### Re: 4 digit no.

I have that abcd=2178.

The limit operator is just an excuse for doing something you know you can't.
“It's the subject that nobody knows anything about that we can all talk about!” ― Richard Feynman
“Taking a new step, uttering a new word, is what people fear most.” ― Fyodor Dostoyevsky, Crime and Punishment

## #3 2012-12-22 05:48:18

bobbym

Offline

### 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 have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

## #4 2012-12-22 06:11:18

jacks
Full Member

Offline

### Re: 4 digit no.

How can i get it.

would you like to explain me

hanks

## #5 2012-12-22 06:20:41

bobbym

Offline

### 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 have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

## #6 2012-12-22 21:53:52

phrontister
Real Member

Offline

### 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

## #7 2012-12-24 02:06:37

jacks
Full Member

Offline

### Re: 4 digit no.

Thanks friends got it