a : 18 = x rest 3 ==> a = 18x + 3
a : 15 = y rest 3 ==> a = 15y + 3
a : 20 = z rest 3 ==> a = 20z + 3
18 = 2 × 3^2
15= 3 × 5
20 = 2^2 × 5
-----------------------
c.m.m.m.c = 2^2 × 3^2 × 5 = 180
a = 180 + 3 = 183 (numarul cautat)
Verificare:
183 : 18 = 10 rest 3
183 : 15 = 12 rest 3
183 : 20 = 9 rest 3