Step-by-step explanation: The odd in favour of something can be calculated as follows

Step 1: Once there are 7 yellow possibilities between 10 possible marbles we have that

Step 2: Once there are 2 red marbles + 1 blue marble = 3 not yellow marbles between 10 marbles we have

Step 3: So the odd in favour of choosing a yellow marble is

Final answer: So the final answer is 7:3