The correct answer is D

Explanation

Choice (D) is correct. Let r be the number of red marbles in the jar. The probability of selecting a red marble is equal to the number of red marbles divided by the total number of marbles. Since the probability of selecting a red marble is 2 over 3, it follows that 2 over 3 = number of red marbles over total number of marbles. There are 36 green marbles and r red marbles, so the previous equation becomes 2 over 3 = r over (r + 36). This simplifies to2(r + 36) = 3r, or 2r + 72 = 3r. Therefore, the number of red marbles, r, is 72.