Notam cele 10 numere consecutive:
a; a+1;a+2;a+3;a+4;a+5;a+6;a+7;a+8;a+9.
Ma = (10×a+1+2+...+9):10 = 8,5
1+2+...+9 = 9×(1+9):2 = 9×10:2 = 9×5 = 45
10×a+45 = 8,5×10
10×a+45 = 85
10×a = 85-45
10×a = 40
a = 40:10
a = 4
a+9 = 4+9 = 13 (cel mai mare numar din cele 10 nr consecutive)