Finding the Heavy Coin by weighing twice Suppose you have $100$ coins. $96$ of them are heavy and $4$ of them are light.  Nothing is known regarding the proportion of their weights. You want to find at least one genuine (heavy) coin. You are allowed to use a weight balance twice. How do you find it?
Assumptions: 
Heavy coins all have the same weight; same for the light coins.
The weight balance compares the weight of two sides on the balance instead of giving numerical measurement of weights.

If you pay me $95$ of the coins in advance I'll show you how ;-).
