A bag holds 8 yellow marbles and 5 orange marbles. How many and what color marbles could you add to the bag so that the probability of picking a yellow is 2/3?
8/13 = 0.615.
The yellow marbles represent less than
2/3 of the total. Therefore, we add X yellow marbles.
(8+x) / 13+x) = 2/3.
Cross multiply:
3x + 24 = 2x 26.
3x - 2x = 26 - 24.
X = 2 Yel. marbles.