Răspuns :
9 + 3 * [7 + 6 * (5 + 4 * a)] : 5 = 60
3 * [7 + 6 * (5 + 4a] : 5 = 60 - 9
3 * (7 + 30 + 24a] = 51 * 5
37 + 24a = 255 : 3
24a = 85 - 37
a = 48 : 24
a = 2
9 + 3 x [ 7 + 6 x ( 5 + 4 x a ) ] : 5 = 60
3 x [ 7 + 6 x ( 5 + 4 x a ) ] : 5 = 60 - 9 = 51
3 x [ 7 + 6 x ( 5 + 4 x a ) ] = 51 x 5 = 255
7 + 6 x ( 5 + 4 x a ) = 255 : 3 = 85
6 x ( 5 + 4 x a ) = 85 - 7 = 78
5 + 4 x a = 78 : 6 = 13
4 x a = 13 - 5
4 x a = 8
a = 8 : 4
a = 2 → numarul aflat prin metoda mersului invers