500 < n < 1000 grupam , imparim , raman ,rest =9 c₁ , c₂ , c₃ caturi n = 18· c₁ + 9 = 20 ·c₂ + 9 = 24·c₂ + 9 scadem 9 n -9 = 18· c₁ = 20 ·c₂ = 24 ·c₃numarul ( n -9 ) = multiplu de 18 ; 20 si 24 18 = 2·3²20 = 2² ·524 = 2³ · 3 --------------------------multiplu = 2³ · 3² · 5 = 8 · 9·5 = 360 n -9 = 360 ; n = 369 solutie falsa 360 ; 720 ; 1080 ,................ multiplii n - 9 = 720 n = 729 elevi