(I) ABC : C = DE - * + (II) AE + AF = DD ---------------------- (III) BGA - FHC = IJ (IV) (V) (VI) Solution: First of all I show that there is no standard solution. That means no leading zero and different letters represent different digits. Assume there were a solution. Then F>=1 from (III) and further B>=2 from (III). Now A>=3 from (IV). With (II) we see D>=2A>=6. But now (VI) shows I >= 2D >= 12 which is too big for a digit in a decimal number system. So we are looking for a non standard solution. When I say A==B, that means A=B (mod 10). (IV.1) E + A == C (III.1) J + C == A (IV.1) + (III.1) E + J == 0 (VI.1) E + D == J (IV.1) + (III.1) + (VI.1) 2E + D == 0 => D is even (II.1) E + F == D (IV.1) + (III.1) + (VI.1) + (II.1) 3E + F == 0 (III) B >= F (IV) A >= B (II) D >= A D >= A >= B >= F (II.2) 2A = D no carry as D>=F (VI) D <= 4 and therefore A <= 2. There are three cases for A. Case A=0, D=0: Then E=F=0 from (II) and I=J=0 from (VI). Then all others letters get zero from (III). Case A=1, D=2: Then E is 4 or 9 from 2E + D == 0. But this contradicts (II). Case A=2, D=4: Then E is 3 or 8 from 2E + D == 0. But this E=8 contradicts (II). The case E=3 gives the only solution. 215 : 5 = 43 - * + 23 + 21 = 44 ---------------------- 192 - 105 = 87 References: J. Petigk, Mathematik in der Freizeit, Aulis Verlag Deubner & Co, Köln, 1998, p151