The Heavy Pill
6.1 The Heavy Pill: You have 20 bottles of pills. 19 bottles have 1.0 gram pills, but one has pills of weight 1.1 grams. Given a scale that provides an exact measurement, how would you find the heavy bottle? You can only use the scale once.
Place n = 1,2,3,... 20 bills respectively from bottles 1,2,3, ... 20 to bottles n+1 = 2,3,4 ... 20. This will give you a hash index into the bottled pill. weight - 210 / .1.