The ratio of the number of chickens in Farm Y to the number of chickens in Farm Z was 3 : 5. There were 42 more chickens in Farm Z than in Farm Y. When 5 chickens escaped from Farm Z, the farmer in Farm Z bought another 20 chickens. What was the new ratio of the number of chickens in Farm Y to the number of chickens in Farm Z in the end? Give your answer in the simplest form.

	Farm Y	Farm Z
Before	3 u	5 u
Change 1		- 5
Change 2		+ 20
After	3 u	5 u + 15

Number of more chickens in Farm Z than Farm Y
= 5 u - 3 u
= 2 u

2 u = 42

1 u = 42 ÷ 2 = 21

Number of chickens in Farm Y
= 3 u
= 21 x 3
= 63

Number of chickens in Farm Z
= 5 u
= 21 x 5
= 105

New number of chickens in Farm Z
= 5 u + 15
= 105 + 15
= 120

Farm Y : Farm Z
63 : 120 _{(÷ 3)}
21 : 40

Answer(s): 21 : 40