Question

(5*a)+(3*b)+(3*c)+(5*d )stiind ca a+b+c+d=20si b+c =9

Answer 1

Restrangi relatia ca sa poti da factor comun
5*a+5*d+3*b+3*c=5(a+d)+3(b+c)=
Din relatia a+b+c+d=20 stii ca b+c=9 rezulta a+9+d=20, a+d =20-9,a+d=11
Revii la prima relatie 5(a+d)+3(b+c)=5*11+3*9=55+27=82