(I) AB * B = CDD : * : (II) CB : B = E ---------------- (III) E * D = BD (IV) (V) (VI) Solution: (II) E != 1 (V) 0 < B <= 3 (II.1) B == B*E (mod 5) => 1 == E (mod 5) Therefore E=6. Then (II) B == 6B (mod 10) => 0 == 5 B (mod 10) That is B is even and we get B=2. (V) D=4 (II) C=1 (IV) A=7 72 * 2 = 144 : * : 12 : 2 = 6 ---------------- 6 * 4 = 24 References: Walter Lietzmann; Lustiges und Merkw\"urdiges von Zahlen und Formen, Verlag Vandenhoeck & Ruprecht, G\"ottingen 1955, 8. Auflage, ISBN 3-525-39112-9 Chap II.5: Vergilbte Manuskripte (p128-131, 21 problems) Chap II.13: Anagramme, Kryptogramme, Geheimschriften und dergleichen (p191-192, 10 problems)