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A bag of marbles contains twice as many red marbles as blue marbles, a 16 Dec 2020, 04:30
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D
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91% (01:11) correct 9% (01:29) wrong based on 96 sessions

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A bag of marbles contains twice as many red marbles as blue marbles, and twice as many blue marbles as green marbles. If these are the only colors of marbles in the bag, what is the probability of randomly picking a blue marble from the bag?

(A) 1/6
(B) 2/9
(C) 1/4
(D) 2/7
(E) 1/3
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D
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A bag of marbles contains twice as many red marbles as blue marbles, a 16 Dec 2020, 07:03
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Bunuel
A bag of marbles contains twice as many red marbles as blue marbles, and twice as many blue marbles as green marbles. If these are the only colors of marbles in the bag, what is the probability of randomly picking a blue marble from the bag?

(A) 1/6
(B) 2/9
(C) 1/4
(D) 2/7
(E) 1/3
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Let the number of green marbles = x, then the number of Blue marbles = 2x and the number of Red marbles = 4x


Total Marbles = x + 2x+ 4x = 7x

Probability = Favorable outcomes / Total Outcomes = 2x / 7x = 2/7


Option D

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A bag of marbles contains twice as many red marbles as blue marbles, a 16 Dec 2020, 10:10
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The bag contains two times the red marbles as blue ones. So, R=2B. It also contains two times the blue marbles as green ones. So, B=2G. So if we consider, G to be 2, we get B as 4 and R as 8.

Now the total outcomes: 14. Chances of getting blue: 4. Hence probability of getting blue: 4/14 = 2/7.

Hence, D is the answer.

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A bag of marbles contains twice as many red marbles as blue marbles, a 18 Mar 2026, 16:59
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Total marbles = x + 2x + 4x = 7x

Blue/total = 2x/7x = 2/7
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A bag of marbles contains twice as many red marbles as blue marbles, a 19 Mar 2026, 18:52
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Let's break this down step by step.

The problem tells us two things:
1. There are twice as many red marbles as blue marbles.
2. There are twice as many blue marbles as green marbles.

The easiest approach is to pick a simple number for green marbles and build from there.

Let's say there are 1 green marble.

Since there are twice as many blue as green:
Blue = 2 × 1 = 2 marbles

Since there are twice as many red as blue:
Red = 2 × 2 = 4 marbles

Now add them all up:
Total = 4 + 2 + 1 = 7 marbles

The probability of picking a blue marble = Blue / Total = 2 / 7

Answer: D

A common mistake here is mixing up the ratios. For example, if you accidentally read it as "twice as many blue as red" (instead of twice as many red as blue), you'd get blue = 4, red = 2, green = 1, and the probability would be 4/7 — which isn't even an answer choice, so that would be a signal to re-read the problem.

Key Principle: When a problem gives you ratios between quantities, assign the smallest group a simple value (like 1) and build the other quantities from there. This makes the math clean and fast.
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