You have 5 jars of pills. Each pill weighs 10 gram, except for contaminated pills contained in one jar, where each pill weighs 9 gm. Given a scale, how could you tell which jar had the contaminated pills in just one measurement?

1. Mark the jars with numbers 1 – 5.
2. Take 1 pill from jar 1, take 2 pills from jar 2, and so on up to jar 5
3. Put all of them on the scale at once and take the measurement.
4. Now, subtract the measurement from 150 = ( 1*10 + 2*10 + 3*10 + 4*10 + 5*10)
5. The result will give you the jar number which has contaminated pill.