When 20% of a number is added to another number the number increases by 50%. What is the respective ratio between the first and the second numbers?

Question: When 20% of a number is added to another number the number increases by 50%. What is the respective ratio between the first and the second numbers?

Solution:
Let the two numbers be x and y

Then,
y + 20% of x = 150% of y
⇒ y + 20x/100 = 150y/100
⇒ y + x/5 = 3y/2
⇒ x/5 = 3y/2 - y
⇒ x/5 = y/2
⇒ x : y = 5 : 2