This blog is highly personal, makes no attempt at being politically correct, will occasionaly offend your sensibility, and certainly does not represent the opinions of the people I work with or for.
Milk and Coffee
I am still amazed by how difficult it is for "normal" people to solve the milk and coffee problem, even though middle school arithmetics is enough to come up with the solution. The sad thing is that scribes of the old Babylon could do that 4000 years ago...


Say that you have two glasses. One has got milk and the other one has got coffee. The two glasses are identical and they have the same amount of liquid in both sides. The two glasses are not full, they just have same amount of liquid. The glass that has coffee will be called the coffee glass and the glass that has milk will be called the milk glass.

You then take a spoon and you use the spoon (a full spoon) to move a spoon of coffee from the coffee glass into the milk glass. At this point you have less coffee into the coffee glass and in the milk glass you have a mix of milk and coffee. You shake the milk glass until the milk and coffee are really mixed and then you use the same spoon to move a full spoon of the mix back into the coffee glass. Both glasses now have the same amount of liquid again, and they both have mixed content. The question now is to choose the glass whose contents is the closest to the original. I want to know whether there is more milk into the coffee glass than coffee into the milk glass.

For the calculus you can use the fact that the glasses had 100 ml of liquid at the beginning and a spoon is 10 ml.