Question

7 grinzi de brad si 12 grinzi de stejar cantaresc impreuna 750kg. 3 grinzi de brad si 8 grinzi de stejar cantaresc impreuna 450kg.Cate kg cantareste o grinda de brad si cate kg cantareste o grinda de stejar

Answer 1

x-grinzile de brad
y-grinzile de stejar

7x+12y=750 |-3
3x+8y=450   |7

-21x-36y=-2250
21x+56y=3150
/ 20y= 900
y=45 kg

7x+12*45=750
7x+540=750
7x=750-540
7x=210
x=30kg.

Answer 2

7b + 12s = 750    | * 3
3b + 8s = 450      | * 7
21b + 36s = 2250
21b + 56s = 3150
le scadem
   /     20s = 900
s = 900 : 20
s = 45 kg are grinda de stejar
3b = 450 - 8 * 45
b = 90 : 3
b = 30 kg are grinda de brad