Răspuns :
(a+b+c)/3=20=> a+b+c=60
b=2a+6
a=c+10
=> b=2(c+10)+6=2c+26, inlocuim pe a si b
=> c+10+2c+26+c=60
4c+36=60
4c=60-36
c=24:4
c=6
a=c+10
a=16
b=2a+6=32+6
b=38
Verificare: (16+38+6):3=60:3=20
                38=2·16+6
                16=6+10
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