Expert: Richard J. Raridon - 5/1/2007

Question
I have found that the answer to ABCD x4=DCBA is 2178=8712, but can you explain it so a 14 year old can understand it please.

Answer
I'm not sure I can explain it so that you can understand it.  The number ABCD can be written 1000A +100B +10C +D
so your equation can be written
4000A +400B +40C +4D = 1000D +100C +10B +A
or 3999A +390B -60C -996D = 0
So you have an indeterminate equation since you have four variables.  However, all is not lost.
You can write it A = (996D+60C-390B)/3999
and you know A has to be an even integer so by playing around with B,C and D you could probably come up with a solution.