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Conditional Probability & Bayes' Theorem · Question 79 of 125

If the ball moved was red, what is the probability that the ball drawn from bag II is red?

Question 79

EasyOriginal question

Bag I has 3 red and 2 black balls; bag II has 2 red and 3 black balls. One ball is drawn at random from bag I and put into bag II without its colour being seen. Then a ball is drawn at random from bag II.

If the ball moved was red, what is the probability that the ball drawn from bag II is red?

Options for question 79

Show the answer and explanation
CorrectNot quiteAnswer C

Correct answer: C

Explanation

  1. After a red ball is moved in, bag II has 3 red and 3 black balls.

  2. 36=12\frac{3}{6} = \frac{1}{2}.

Worth noting

25\frac{2}{5} uses bag II as it was, forgetting the ball moved into it.

Concept
A bag changed by an earlier draw
Typical time
90 s
Your time
—
The rule this testsThe theorem of total probability
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Ten questions from Conditional Probability & Bayes' Theorem, at your own pace.

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Ten questions from Conditional Probability & Bayes' Theorem, at your own pace.

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