n = numarul napolitanelor din cutie (n ≤ 450)
=> n:5 = ... (rest 4) adica n=M₅+4
n:6 = ... (rest 4) ,, n=M₆+4 si
n:7 = ... (rest 4) ,, n=M₇+4
iar n:8 = ... (rest 0)
=> n-4 = [5;6;7] = 210 ⇒ n = M₂₁₀+4 = {1*210+4=214 ; 2*210+4=424 ; .....}
deci n = 424 .
Verificare: 424:5=84 (rest 4) ; 424:6=70 (rest 4) ; 424:7=60 (rest 4) si 424:8=53 .