Backsolving

[stripes123]

Hi, with this problem I understand how to backsolve, but when we use 1200 for example and get X 300, Y is 900, then take 100 away from both and get 200 and 800 respectively. in the video we see ok this makes Y 4* x instead of 3 times. how do you know from there that all the smaller answers will be wrong (i.e. answer must be A) without backsolving that too?

[Leaderboard]

You can reason that as you increase the amount of fuel, the ratio of the amount of fuel of X and Y should be lower.

It doesn’t take that much time to backsolve every option though.