Brain Teasers
A Card Puzzle
Probability
Probability puzzles require you to weigh all the possibilities and pick the most likely outcome.Probability
I have ten cards 1-10.
I turn three facedown.
I turn the 2 and 8 faceup.
What is the probability of drawing a 1?
I turn three facedown.
I turn the 2 and 8 faceup.
What is the probability of drawing a 1?
Answer
1/8Facedown cards do not effect the probability.
For example:
I have three cards and I turn one facedown.
There is a 1/3 chance that the 1 card is facedown...
1/3(1/1)+2/3(0/2)=1/3
...and a 2/3 chance that it isn't:
1/3(0/1)+2/3(1/2)=1/3
Both have the same probability.
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