Answer:
red : blue = 2 : 1
Step-by-step explanation:
It is convenient to write the ratios so that the number representing green marbles is the same in both cases.
red : green = 3 : 1 = 6 : 2
Then we have ...
red : green : total = 6 : 2 : 11
The number of ratio units for blue marbles is then 11 -6 -2 = 3, so we have ...
red : green : blue : total = 6 : 2 : 3 : 11
Then red : blue = 6 : 3 = 2 : 1