Brain teaser 1:

Problem set up:

You have two bottles: a 5 liter bottle and a 3 liter bottle. The 3 liter bottle does not fit inside the 5 liter bottle.
The bottles do not have any markings, like measuring cylinders have, for any other volume other than full 5 liters for the 5 liter bottle and full 3 liters for the 3 liter bottle.

You are preparing cement at your summer house to fix the cracking window sills. You need to measure exactly 4 liters of water from a lake to prepare the cement. How do you use the 5 and 3 liter bottles to measure exactly the needed 4 liters of water. You are also required to have the 4 liters of water in the 5 liter bottle before you pour it on the mixture. You may take water from the lake as many times you like as long as in the end you have 4 liters in the 5 liter bottle.

Note: There are at least two different solutions to the problem.

Brain teaser 2:

Problem set up:

There is a windowless room with only one door. Inside the room there are three identical light bulbs. From each light bulb there is an electric wire leading to a switch which is located outside the room, i.e. there are three switches outside the room. The electrician making the connections has made a mistake: the electrician does not know which switch belongs to which light bulb.

Your task is to find out which switch operates each light bulb.The rules that you must obey in your task are:
  • In the beginning all the light bulbs are in an off-position.
  • During the task you are allowed to enter the room only once. This means that you will see the light bulbs only once.
  • Once you are inside the room you may do there what ever you like to do.
  • You may do whatever you like with the switches before you enter the room or after you have exited the room.
  • You are not able to see inside the room at the same time when you work the switches as the door will be closed before and after you have visited the room.

Brain teaser 3:

Problem set up:

You have a bag of gold coins. All the coin are real and identical except one. One coin looks like the others but is not made of gold. You do not know if the fake coin is made of material that is more or less dense than gold, i.e. you do not know wheather it will weigh more or less than real coins.

Your task is to find out the minimum number of measurements to be made to find out:
  1. which coin is the fake coin or,
  2. which coin is the fake coin and wheather it is heavier or lighter than the real ones.

You are allowed to use a simple balancing scale. external image balance.jpg

Try to solve the case when you have 3, 4, 5, .... coins.

Crater simulator

This impact calculator will show you what happens when an asteroid hit the Earth. You may change several variables - have a go and have fun!


  • Build as tall structure as you can.