2 + [ 4 + ( 20 + a ) : 5 ] : 3 = 5
[ 4 + ( 20 + a ) : 5 ] : 3 = 5 - 2
[ 4 + ( 20 + a ) : 5 ] : 3 = 3
4 + ( 20 + a ) : 5 = 3 × 3 = 9
( 20 + a ) : 5 = 9 - 4
( 20 + a ) : 5 = 5
20 + a = 5 × 5
20 + a = 25
a = 25 - 20
a = 5 → numarul, aflat prin metoda mersului invers
Verific:
2 + [ 4 + ( 20 + 5 ) : 5 ] : 3 = 2 + ( 4 + 5 ) : 3 =2 + 9 : 3 = 2 + 3 = 5
