Hi in this problem from GRE mini test 10, I don’t understand why the ratio of A/B is 4/5 and not 5/4 when in the picture it’s showing difference in original percentage and new percentage of A is 5? Can anyone please explain the concept properly? Thanks

Hi,

So how this method works is, let’s assume the number 30 as C.

Now in order to obtain C, ratio of A & B mixed should be (B-C):(A-C).

Basically the subtracted numbers are switched to obtain the new ratio.

As this is a shortcut trick the logic behind this is little bit long, I suggest you to keep this 2 steps in mind as they are pretty simple.

Thanks! Is there any materials available in Gregmat or elsewhere to understand the concept?

Im not sure if Greg has explained this method in his concept classes, but a scholar has explained it step by step in Test Your GRE Quant concepts - 5th July 2022 from 21:25. Logic behind this isn’t cleared but this might help you.