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a+b=10 si b+c=20 atunci 2a+5b+3c cu cat este egal

Răspuns :

2a+5b+3c =
2a+2b+3b+3c=
2(a+b)+3(b+c)=
2*10+3*20=
20+60=80
a+b= 10
b+c= 20
2a+5b+3c=2a+2b+3b+3c= 2(a+b)+3(b+c)=2*10+3*20=20+30=80