Answer:
3 red, 2 blue and 4 green marbles.
Step-by-step explanation:
Presently the bag contains 18 marbles.
Probability of selecting a red marble in the bag of 18 marbles = 6/18 = 1/3.
Probability of getting a blue is 2/9 and of getting green is 4/9.
So if we have 27 marbles the probability of a red must be 1/3 so we must have 1/3 * 27 = 9 reds.
In a similar calculation there would have to be 2/9 * 27 = 6 blues and
4/9 * 27 = 12 green marbles.
So we have to add 9-6 = 3 red, 6-4 = 2 blue and 12-8 = 4 green marbles.
