Answer:
16.7%.
Explanation:
In this case, we know that although the marble is selected, it is replaced, that is, the total value of marbles never changes. 
We know that in total there are 6 (3 + 2 + 1) 
The probability of drawing a red is: 
3/6 
The probability of getting a yellow is: 
2/6 
Therefore the probability of drawing a red and a yellow is: 
3/6 * 2/6 = 6/36 = 1/6 = 0.167 
In other words, the probability of this happening would be 16.7%.