In a container, there are x black marbles and y white marbles. A marble is selected at random from the container and not put back. Then, another marble is selected at random from the remaining marbles. What is the probability that the first marble selected is black and the second marble selected is white?

Answer Choices

Correct answer marked below

\frac{x}{x+y}*\frac{y}{x+y-1}

Correct

\frac{x}{x+y}*\frac{x-1}{x+y-1}

\frac{xy}{x+y}

\frac{x-1}{x+y}*\frac{y-1}{x+y}

\frac{x}{x+y}*\frac{y}{x+y}

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Explanation

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Official Explanation

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Given: • A container holds x black marbles and y white marbles • A marble is drawn at random and not replaced • A second marble is then drawn from the remaining marbles To find: • The probability that the first marble drawn is black and the second marble drawn is white Approach and Working: • The probability that the first drawn marble is…

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Comments

BadalApr 21, 2025

This is definitely a test-day trap

RubenDec 5, 2024

Great!

What this question tests

What it tests

Your ability to compute probabilities of single and compound events, including 'at least one' questions.

Common trap

Forgetting to use the complement for 'at least one', or treating dependent events as independent.