Answer: 4 kids get an apple (one apple for each one of them) and the fifth kid gets an apple with the basket still containing the apple.
Answer: Keep the first bulb switched on for a few minutes. It gets warm, right? So all you have to do then is … switch it off, switch another one on, walk into the room with bulbs, touch them and tell which one was switched on as the first one (the warm one) and the others can be easily identified …
Answer: Fill the 5-litre bowl and overspill water to the 3-litre bowl, which you empty afterwards. From the 5-litre bowl overspill the 2 remaining litres to the 3-litre bowl. Refill the 5-litre bowl and fill in the 3-litre bowl (with 1 litre), so there stay the 4 required litres in the 5-litre bowl.
Answer: You can turn a square manhole cover sideways and drop it down the diagonal of the manhole. You cannot drop a round manhole cover down the manhole. Therefore, round manhole covers are safer and more practical than square ones.
Answer: There is a complicated way counting a sequence. Or simply knowing that if the fly is flying the 2 hours still at the same speed of 75 km/h then it flies a distance of 150 km.
Answer: You can put one foot-bridge over one corner (thus a triangle is created). Then from the middle of this foot-bridge lay another foot-bridge to the edge (corner) of the castle. You can make a few easy equations confirming that this is enough.
Answer: When the trains encounter, they will be approximately the same distance away from New York. The New York train will be closer to New York by approximately one train length because they’re coming from different directions. That is, unless you take “meet” to mean “perfectly overlap”.