Two numbers are respectively 20% and 50% more than a third number. The ratio of the two numbers is:

Let the third number be x.
Then, first number = 120% of x =120x/100 = 6x/5  

Second number =150% of x = 150x/100 = 3x/2
Ratio of first two numbers = 6x/5 : 3x/2 = 12x : 15x = 4 : 5