Răspuns :
Metoda mersului invers
100-[(x+21):21-21] = 1
(x+21):21-21 = 100-1
(x+21):21-21 = 99
(x+21):21 = 99+21
(x+21):21 = 120
x+21 = 120·21
x+21 = 2520
x = 2520-21
[tex]x = 2499[/tex]
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Proba: 100-[(2499+21):21-21] = 100-[2520:21-21] = 100-[120-21] = 100-99 = 1 (corect)