Răspuns :
{[(a-5)÷5]+1}×4}=80
{[(a-5)÷5]+1}=80÷4
{[(a-5)÷5]+1}=20
[(a-5)÷5]=20-1
[(a-5)÷5]=19
(a-5)=19×5
(a-5)=95
a=95+5
a=100
{[(a-5)÷5]+1}=80÷4
{[(a-5)÷5]+1}=20
[(a-5)÷5]=20-1
[(a-5)÷5]=19
(a-5)=19×5
(a-5)=95
a=95+5
a=100
Facem totul invers 80:4=20 20-1=19 19*5=95 95+5=100 Mihai sa gindit la numarul 100