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

a = grinda brad
b = grinda stejar

7a + 12b = 750
3a + 8b =450 => 3a = 450 - 8b => a = (450-8b) : 3

inlocuim a in prima ec
=> 7(450-8b) : 3 + 12b = 750
aducem la acelasi numitor
3150 - 56b + 36b = 2250
20b = 3150-2250=900
b=45
a=(450-8x45):3 = (450-360):3=90:3=30
a=30