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(a+a+1+a+2):20=4 rest 13

Răspuns :

(a*3+3):20=4 rest 13
a*3+3=20*4+13
a*3+3=93/-3
a*3=90
a=30
(3a+3):20=4 rest 13
3a+3=20x4+13
3(a+1)=93
a+1=93/3
a+1=31
a=31-1
a=30