45 - 2 × { 17 + 14 : [ 27 - ( 15 + a ) ] - 3 } = 3
2 × { 17 + 14 : [ 27 - ( 15 + a ) ] - 3 } = 45 - 3
2 × { 17 + 14 : [ 27 - ( 15 + a ) ] - 3 } = 42
17 + 14 : [ 27 - ( 15 + a ) ] - 3 = 42 : 2
17 + 14 : [ 27 - ( 15 + a ) ] - 3 = 21
17 + 14 : [ 27 - ( 15 + a ) ] = 21 + 3
14 : [ 27 - ( 15 + a ) ] = 24 - 17
14 : [ 27 - ( 15 + a ) ] = 7
27 - ( 15 + a ) = 14 : 7
27 - ( 15 + a ) = 2
15 + a = 27 - 2
15 + a = 25
a = 25 - 15
a = 10 → numarul, aflat prin metoda mersului invers
