The ratio of present ages of X and Y is 4:5. Which of the following can't be the ratio of ages of X and Y, 20 years ago ?

A 2 : 5

B 8 : 15

C 9 : 10

D 3 : 5

Correct Answer: Option C

The ratio of X and Y ages at present is 4:5.

Then, the ratio 20 years ago will not be more than the ratio at present.

So, from the options 9:10 is not satifying => its ratio is 0.9 which is greater than presnt ratio of 0.8.