Răspuns: a = 84
Explicație pas cu pas:
[ ( a : 7 + 69 ) : 9 + 71 ] : 20 + 8 = 12
[ ( a : 7 + 69 ) : 9 + 71 ] : 20 = 12 - 8
[ ( a : 7 + 69 ) : 9 + 71 ] : 20 = 4
( a : 7 + 69 ) : 9 + 71 = 4 × 20
( a : 7 + 69 ) : 9 + 71 = 80
( a : 7 + 69 ) : 9 = 80 - 71
( a : 7 + 69 ) : 9 = 9
a : 7 + 69 = 9 × 9
a : 7 + 69 = 81
a : 7 = 81 - 69
a : 7 = 12
a = 12 × 7
a = 84 → numarul, aflat prin metoda mersului invers
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Verific:
[ ( 84 : 7 + 69) : 9 + 71] : 20 + 8 =12
= ( 81 : 9 + 71) : 20 + 8 =
= 80 : 20 + 8 =
= 4 + 8 =
= 12
