Question of the Day

Can you answer today's question?

Register Next Tests:
6/1

Jan

25

2013

342,256 responses

Question of the Day Statistics
	Number Answered
Correct	164,254
Incorrect	178,002

47% correct

Mathematics > Standard Multiple Choice

Read the following SAT test question and then click on a button to select your answer.

A jar contains only red marbles and green marbles. If a marble is selected at random from the jar, the probability that a red marble will be selected is 2 over 3 . If there are green marbles in the jar, how many red marbles are there in the jar?

Hint

The probability of selecting a red marble, 2 over 3 , is equal to the number of red marbles divided by the total number of marbles.

Question of the Day

Can you answer today's question?

Register Next Tests:
6/1

Jan

25

2013

342,256 responses

Question of the Day Statistics
	Number Answered
Correct	164,254
Incorrect	178,002

47% correct

Mathematics > Standard Multiple Choice

Read the following SAT test question and then click on a button to select your answer.

A jar contains only red marbles and green marbles. If a marble is selected at random from the jar, the probability that a red marble will be selected is 2 over 3 . If there are green marbles in the jar, how many red marbles are there in the jar?

Answer

Choice (D) is correct. Let 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 green marbles and red marbles, so the previous equation becomes 2 over 3 = r over (r + 36) . This simplifies to 2 times (r plus 36) equals 3 times r , or (2 times r) plus 72 equals 3 times r . Therefore, the number of red marbles, , is .