Ratio
posted by Mary .
The Ratio of the hieght of plant X to plant Y is 5:3. If plant Y were 140 c.m. taller instead, the ratio of the hieght of plant X to plant Y would be 1:2. How tall is plant X

Translate these info into equations:
y=3/5x
x=5/3y
y+140=2x
Now you can use substitution method to solve for x easily. 
alternate solution:
let the height of pant X be 5x
let the height of plant Y be 3x
5x/(3x+140) = 1/2
10x = 3x+140
x= 20
then X = 5x = 100
Y = 3x = 60
check : if 140 is added to 60, Y = 200
then X:Y = 1:2