There are three bags, each containing two marbles. Bag A contains two white marbles, Bag B contains two black marbles, and Bag C contains one white marble and one black marble. You pick a random bag and take out one marble, which is white. What is the probability that the remaining marble from the same bag is also white?
Riddles for Scholars
The best hard riddles for scholars.
There is a barrel with no lid and some wine in it. “This barrel of wine is more than half full,” says the woman. “No, it’s not,” says the man. “It’s less than half full.” Without any measuring implements and without removing any wine from the barrel, how can they easily determine who is correct?
This famous river crossing problem is known as the “bridge and torch” puzzle. Four people are crossing a bridge at night, so they all need a torch—but they just have one that only lasts 15 minutes. Alice can cross in one minute, Ben in two minutes, Cindy in five minutes and Don in eight minutes. No more than two people can cross at a time; and when two cross, they have to go at the slower person’s pace. How do they get across in 15 minutes?
Dynamite is a tool that can be used to cut down trees. To cut a tree 18 inches in diameter requires five sticks of dynamite: one on the north, south, east and west sides of the tree, and the fifth stick on the side to which the tree should fall. During construction of a dam, a tree 18 inches in diameter was completely covered by water. Since the treetop was fouling the boat's propellers, it had to be cut down. A diver went down and put a stick of dynamite on the four sides of the tree. Since the current is flowing south at 2 knots per hour, on which side of the tree would you instruct the diver to put the fifth stick of dynamite if you wanted the tree to fall north?
Which clock works best, the one that loses a minute a day, or the one that doesn't work at all?
How many 1 foot by 1 foot bricks would it take to complete a building that's 20 feet long on all four sides and 20 feet high?
Three working women have different careers. If only one of statements 1, 2 and 3 are true, can you tell whether or not Mary is a nurse? 1. This statement is only true if statement 5 is false. 2. This statement is true if statements 4 or 5, or both 4 and 5 are true. 3. This statement is false only if both statements 6 and 1 are true. 4. Mary is a nurse 5. Karen is an artist. 6. Sarah is a photographer.