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- You have a 100 coins laying flat on a table, each with a head side and a tail side. 10 of them are heads up, 90 are tails up. You can't feel, see or in any other way find out which side is up. Split the coins into two piles such that there are the same number of heads in each pile.
- You have 7 cards: two are red on both sides, two are black on both sides, and three are red/black. You choose a card at random, and one of its sides is red. What is the probability that the other side is also red?
- You have two ropes, and each takes exactly one hour to burn. How would you use them to time exactly 15 minutes? Note that the ropes are of uneven densities, so half the rope length-wise does not necessarily take half an hour to burn.
- You have a birthday cake and have exactly 3 cuts to cut it into 8 equal pieces. How do you do it?
- 100 Smurfs and Gargamel problem.
- Desert crossing problem.
- Collection of coin questions
- Three closed boxes have either white marbles, black marbles or both, and they are labeled white, black and both. However, you’re told that each of the labels are wrong. You may reach into one of the boxes and pull out only one marble. Which box should you remove a marble from to determine the contents of all three boxes?
- A grocer proposed to put up 20 lbs of tea into 2-lb packets, but his weights had been misplaced by somebody and he could only find the 5-lb and the 9-lb weights. What is the quickest way for him to do the business?