Stiind ca a+b=12,b+c=45,
c+a=251,calculati (a+b+c):2.

Răspuns
a+b+b+c+c+a=12+45+251
2(a+b+c)=308=>a+b+c=308:2=>a+b+c=154
(a+b+c):2=154:2=77