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

You are not logged in.

- Topics: Active | Unanswered

Pages: **1**

**jacks****Member**- Registered: 2012-11-21
- Posts: 77

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

Offline

**anonimnystefy****Real Member**- From: The Foundation
- Registered: 2011-05-23
- Posts: 15,397

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

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 84,614

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.**

Offline

**jacks****Member**- Registered: 2012-11-21
- Posts: 77

Yes 2178 is right answer.

How can i get it.

would you like to explain me

hanks

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 84,614

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.**

Offline

**phrontister****Real Member**- From: The Land of Tomorrow
- Registered: 2009-07-12
- Posts: 3,843

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

Offline

**jacks****Member**- Registered: 2012-11-21
- Posts: 77

Thanks friends got it

Offline

Pages: **1**