Natalya put 14 blue marbles, 14 red marbles, and no other marbles into 3 empty cups. She put 2 blue...
GMAT Two Part Analysis : (TPA) Questions
Natalya put 14 blue marbles, 14 red marbles, and no other marbles into 3 empty cups. She put 2 blue marbles and 6 red marbles in Cup A, 6 blue marbles and 4 red marbles in Cup B, and 6 blue marbles and 4 red marbles in Cup C.
After this, Dmitry will randomly pick three marbles, one from each cup. Consistent with the given information, select for 3 blue the probability that Dmitry will pick 3 blue marbles, and select for 3 red the probability that Dmitry will pick 3 red marbles. Make only two selections, one in each column.
Let's visualize this problem to make it crystal clear.
Phase 1: Owning the Dataset
Visualization
Let's create a simple table to organize our marble distribution:
Cup | Blue Marbles | Red Marbles | Total |
A | 2 | 6 | 8 |
B | 6 | 4 | 10 |
C | 6 | 4 | 10 |
Total | 14 | 14 | 28 |
We can verify our totals: \(2+6+6 = 14\) blue ✓ and \(6+4+4 = 14\) red ✓
Phase 2: Understanding the Question
Dmitry will randomly pick exactly one marble from each cup. We need to find:
- 3 Blue: The probability that all three marbles picked are blue
- 3 Red: The probability that all three marbles picked are red
Since he picks one marble from each cup independently, we'll multiply the individual probabilities.
Phase 3: Finding the Answer
Calculating P(3 Blue Marbles)
For Dmitry to pick 3 blue marbles, he needs:
- A blue marble from Cup A: \(\mathrm{P} = \frac{2}{8} = \frac{1}{4}\)
- A blue marble from Cup B: \(\mathrm{P} = \frac{6}{10} = \frac{3}{5}\)
- A blue marble from Cup C: \(\mathrm{P} = \frac{6}{10} = \frac{3}{5}\)
Combined probability:
\(\mathrm{P(3\,blue)} = \frac{1}{4} \times \frac{3}{5} \times \frac{3}{5} = \frac{9}{100} = 0.090\)
Calculating P(3 Red Marbles)
For Dmitry to pick 3 red marbles, he needs:
- A red marble from Cup A: \(\mathrm{P} = \frac{6}{8} = \frac{3}{4}\)
- A red marble from Cup B: \(\mathrm{P} = \frac{4}{10} = \frac{2}{5}\)
- A red marble from Cup C: \(\mathrm{P} = \frac{4}{10} = \frac{2}{5}\)
Combined probability:
\(\mathrm{P(3\,red)} = \frac{3}{4} \times \frac{2}{5} \times \frac{2}{5} = \frac{12}{100} = 0.120\)
Phase 4: Solution
Based on our calculations:
- 3 Blue: 0.090
- 3 Red: 0.120
These values match the answer choices provided, confirming our analysis.