Question 96
HardOriginal questionBag 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.
The ball drawn from bag II is red. What is the probability that the ball moved was red?
Show the answer and explanation
CorrectNot quiteAnswer D
Correct answer: D
Explanation
Let be that the ball moved is red and that the ball drawn is red: , and .
.
Worth noting
is the chance that the ball moved was red before the drawn ball is seen; a red draw makes it likelier.
- Concept
- Bayes' theorem
- Typical timeTypical
- 150 s
- Your timeYours
- —
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