Đáp án:
`a)`
` x/2 = y/5 = (x+y)/7 = 70/7 = 10`
` => x = 20 ; y =50 ; z =70`
`b)`
` x/7 = y/3 = (x-y)/4 = 24/4 = 6`
` => x= 42; y = 18`
`c)`
` x/5 = y/4 = z/6 = k`
` => x =5k ; y = 4k ; z = 6k`
` => xyz = 5k.4k.6k = 960`
` => k^3 = 8`
` => k =2`
` => x =10 ; y= 8y ;z = 12`