a)
25x/100 =30y/100 ⇒ 25x=30y⇒ 5x=6y
60y/100 = 80z/100⇒ 60y=80z⇒ 3y=4z
5x=2*3y=2*4z=8z⇒ x=8z/5
y=4z/3
x+y= 8z/5 + 4z/3 = (24z + 20z)/15= 44z/15= 44/15 *z
44/15=a/100⇒ a=4400:15= 293, (3) %
x+y= 293, (3) % din z
b) 5x/100 + 10y/100 +15z/100= 50y/100 - 10
(5x+10y+15z)/100 = (50y-1000)/100
5x+10y+15z = 50y-1000
1000 = 50y-5x-10y-15z
1000=40y-5x-15z /:5
200 = 8y -x -3z
200=8y - 6y/5 - 9y/4
200 = (160y-24y-45y) :20
200*20 = 91y
4000=91y⇒ y=4000/91
x= 6*4000/91*5=6*800/91= 4800/91
z=3*4000/91*4= 3*1000/91=3000/91
