a : 12 = X rest 3 ==> a = 12X+3
a : 20 = Y rest 3 ==> a = 20Y+3
a : 30 = Z rest 3 ==> a = 30Z +3
12 = 2^2 × 3
20 = 2^2 × 5
30 = 2 × 3 × 5
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c.m.m.m.c = 2^2 × 3 × 5 = 60
a = 60 + 3 = 63 (numarul cautat)
Verificare:
63 : 12 = 5 rest 3
63 : 20 = 3 rest 3
63 : 30 = 2 rest 3