Solution 1: given that X: Y: z = 3:4:5, and 3x-4y + Z = - 4, find the value of formula x-3y + 5Z. 2 a batch of manuscripts, a copy 30 hours, B copy 20 hours, now from a copy 3 hours later to B copy the rest, ask B how many hours still need to copy (equation solution)

Solution 1: given that X: Y: z = 3:4:5, and 3x-4y + Z = - 4, find the value of formula x-3y + 5Z. 2 a batch of manuscripts, a copy 30 hours, B copy 20 hours, now from a copy 3 hours later to B copy the rest, ask B how many hours still need to copy (equation solution)

1,x：y：z＝3：4：5,
So 4x = 3Y, 5x = 3Z, x = 3Z / 5, 5Y = 4Z, y = 4Z / 5
2,3x-4y＋z＝-4
9z/5-16z/5+z=-4
-2z/5=-4
z=10
So x = 6, y = 8, z = 10
2. There is no need to set up equations
A 30 hours, so copy 1 / 30 every hour
Similarly, B is 1 / 20 an hour
A copy 3 hours, 3 / 30 = 1 / 10, copy 1 / 10 of the total
So B has only 9 / 10 of the total, 20 x 9 / 10 = 18 hours
Let B take x hours
X / 20 + 3 / 30 = 1 gives x = 18