1. Time to Burn
Picture yourself with two ropes and a lighter in your hands. It takes each rope exactly one hour to burn from one end to the other, besides, the speed of burning is not uniform throughout the whole hour. How can you measure exactly 45 minutes with the help of this tricky equipment?
Solution: Light both ends of the first rope and only one end of the other rope. Since it is burning from both ends, the first rope will be gone in 30 minutes - half the time it takes both ropes to burn completely. Then light the other end of the other rope and watch it burn completely in 15 minutes.
2. Cork a Coin
There’s an empty bottle on the table. You put a coin into the bottle and close it with a cork. Now you have to remove the coin without uncorking or breaking the bottle. How will you do it?
Solution: Push the cork into the bottle and shake the coin out!
3. Pot of Gold
You received a very strange windfall: it consists of 100 pots, each with 100 coins inside, but only one of them contains real gold coins. A plain metal coin weighs 1 ounce, and a gold coin is .01 ounce heavier. How can you find the pot of gold, if the only equipment you have is a scale, which is already on its last legs and can only be used once?
Solution: Resort to arithmetic sequences: take 1 coin from the first pot, 2 coins from the 2nd pot, 3 coins from the 3rd pot and so on up to 100 coins from the last pot. Weight the pile and do a little math: subtract 5,050 oz from the total weight and look at the last two figures of the answer to get the number of the pot your gold is in!
4. Green Thumb
You bought 7 apple saplings. How can you plant them in your garden to make six straight rows of three trees each?
Solution: You need a designer solution: plant the trees in the shape of an equilateral triangle with three saplings making the corners, three other marking the midpoints of the sides, and the final sapling placed in the center.
5. Chief Culprit
Liam, Michael, and Jacob were brought to the police station and questioned in connection with a bank robbery. They all gave different statements, but only one of the three is to blame. Liam said he was innocent. Michael insisted on being innocent as well. And Jacob blamed everything on Michael. However, only one of the men told the truth. The question is: Who had robbed the bank, then?
Solution: If Liam is telling the truth, it means that Michael and Jacob are both lying. But it makes Michael guilty and innocent at the same time, which is impossible. If Jacob is telling the truth, it means both Liam and Michael are to blame, but it contradicts the condition of a single culprit. Therefore, Michael’s statement is true, which makes Liam a liar and a robber.