Monday, May 11, 2009

Three cards

Here is a puzzle suggested to me by one of the dads at the school soccer practice:

You have three cards: each has two colored sides.
One with both sides colored red.
Second with both sides green.
And a third with one side green and one red.

You close your eyes and pick one of the cards. You open your eyes and see that the side pointing to you is green. What are the chances of the back side of this card being red?


Anonymous said...

As i am seing a side with GREEN colour, so it can't be the card with both sides RED.
so it can be any one of GREEN-GREEN or GREEN-RED card. So in total there are 3 GREEN sides, so there are total 3 possibilities, out of which in one case the other side is RED. So the probability is 1/3


Maria said...

Wow, Rakhel!
You seem to be a pro.
This was a tricky puzzle. Very similar to the "three doors" or Monty Hall puzzle that confused people for many many years.

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