BunuelCould it be solved this way?
- 500 Resp and 600 Demo joined the registration
- the number of people "behind" the ratio is stable (I mean what amount of people 1 Resp and 1 Demo in the ratio represent)
- from the final ratio 4/5 we see that the difference is just one "number behind the ratio"
- since joined 500 resp and 600 demo do not convert ratio to irrational (like 4.12/5.06) we conclude that the "number behind the ratio" is a multiple of 5 and 6
- so we have steps of 30 people to represent "the number behind the ratio" (it could be 30, 60, 90, 120, 150... 300... 600... and so on).
- do not plug these values into the ratio. Just see what number from the answer choices represent multiple of 30.
- only B fits.