Răspuns:
n = 47
Explicație pas cu pas:
n = numarul natural
n-12
(n-12):5
(n-12):5 + 7
[(n-12):5 + 7]·2 = 28 <=>
---------------
(n-12):5 + 7 = 28:2 <=>
(n-12):5 + 7 = 14 <=>
(n-12):5 = 14-7 =>
(n-12):5 = 7 =>
n-12 = 7·5 =>
n-12 = 35 =>
n = 35 + 12 =>
n = 47
Verificare :
[(47-12):5+7]·2 = (35:5+7)·2 = (7+7)·2 = 14·2 = 28 , corect