a+ b= 24
b+ 3·c= 31
_______________
3·a+ 5·b+ 6·c= ?
Obs. Înmulţirea = adunare repetată
3·a = a+ a+ a
5·b = b+ b+ b+ b+ b
6·c= c+ c+ c+ c+ c+ c
3·a+ 5·b+ 6·c=
a+ a+ a + b+ b+ b+ b+ b+ c+ c+ c+ c+ c+ c =
Obs. Se grupează!
(a+ b) + ( a+ b) + ( a+ b) + ( b+ +c+c+c) + ( b+ c+ c+ c) =
(a+ b) + ( a+ b) + ( a+ b) + ( b+ 3·c) + ( b+ 3·c)=
24 + 24+ 24+ 31+ 31=
24·3+ 31·2=
72+ 62=
134
