Another Silly Riddle for you guys

DaShen

Lifer
Dec 1, 2000
10,710
1
0
ABCD * 4 = DCBA

A = ?
B = ?
C = ?
D = ?

It is easy once you think about it. But it is fun to think about this kind of stuff. And for you CS guys (no it is not Hexadecimal). ;)

BTW... it is not 0000 * 4 = 0000
It is actual numbers other than zero.
 

eLiu

Diamond Member
Jun 4, 2001
6,407
1
0
2178

edit: 4*D = A mod 10. Also A<3 else you get 5 digits. So A = 2, D = 8 is the only choice.

Then (4*C+3) = B mod 10 because 8*4=32, so you carried a 3. Again B < 2 else the carry-over will change the 1000s place.

From there, C = 7, B = 1.
 

Leros

Lifer
Jul 11, 2004
21,867
7
81
As eLiu pointed out, the other answer is 2178.

I just wrote a program to test all possible solutions. Seemed easier than thinking about it.
 

thesurge

Golden Member
Dec 11, 2004
1,745
0
0
Extension:
AB....4*4=4AB.... (Ex. AB.....4--->4AB.... as 1234--->4123)

AB..... and 4AB....each represent a distinct integer (with digits A,B etc.).

find AB....
 

dlock13

Platinum Member
Oct 24, 2006
2,806
2
81
This is the kind of question we get on these lame "Math League" tests. There are six questions which seem hard, but once given the solution, they are rather simple.

I personally like the challenge.
 

DaShen

Lifer
Dec 1, 2000
10,710
1
0
Originally posted by: eLiu
2178

edit: 4*D = A mod 10. Also A<3 else you get 5 digits. So A = 2, D = 8 is the only choice.

Then (4*C+3) = B mod 10 because 8*4=32, so you carried a 3. Again B < 2 else the carry-over will change the 1000s place.

From there, C = 7, B = 1.

Correct sir.

BUMP for work crowd