Question

stiind că a+b=10 si b+c=12 , calculează 3•a+7•b+4•c

Answer 1

a+b=10
b+c=12
Alegem factorul comun
(3•a+3•b)+(4•b+4•c)=
3•(a+b)+4•(b+c)=
3•10+4•12=
30+48=
78

Answer 2

$3 \times a + 7 \times b + 4 \times c = \\ \\ 3 \times a + (3 \times b + 4 \times b) + 4 \times c = \\ \\ (3 \times a + 3 \times b) + (4 \times b + 4 \times c) = \\ \\ 3 \times 10 + 4 \times 12 = \\ \\ 30 + 48 = 78$