Answer:
1:3
Explanation:
To find the probability of selecting a certain type of item from a collection, simply divide the number of items of that type by the total number of items.
There are 3 + 2 + 1 = 6 marbles in total. There are 2 yellow marbles, so the probability of choosing a yellow marble on the first draw is 2/6. This can be further simplified to 1:3.