How should you saw a block of stone of 40 kg into four pieces such that you can measure all weights of an integer from 1 kg to 40 kg (so 1 kg, 2 kg, 3 kg, 4 kg, ..... 39 kg and 40 kg) on a balance?

Sarah and Mike conclude that it is wednesday. But five minutes later it is already friday. How is that possible?

At the same time two planes depart from JFK international airport. One plane flies exactly in northern direction, while the other one flies exactly to the east. Both planes fly at the same speed and at the same height. Which plane is after one hour the most far away from JFK?