ABCDE X 4 = EDCBA
Assume that A, B, C, D and E can only be one of ten numbers 0,1,2,...,9. We solve this equation as follows.
Since ABCDE *4=EDCBA (*)
we know that A must be an even number, i.e, A may be 0,2,4,6,8. Obviously, A can't be 4,6,8 since otherwise, ABCDE*4>100000 which is impossible. So we consider the following two cases.
By (*) we know that E=8. So we can write (*) as follows.
This shows how to assign numbers to letters in a multiplication problem.