There are eight pills. They are all the same size and color. One pill weighs slightly more than the others and it is poisonous. You have a balanced scale and can only use it twice. How can you find the poisoned pill?
Split the pills into 3 groups – 2 groups with 3 pills each and 1 group with 2 pills.
Now put the 2 groups of 3 pills on the scale.
Scenario #1: Both groups weigh the same. This means that the poisonous pill is in the group with 2 pills. So take the 2 pills from that group and use the scale to determine the poisonous pill.
Scenario #2: One group weighs more than the other. Take any 2 pills from this group of 3 pills. If they weigh the same, then the 3rd pill is the poisonous pill. If they don’t weigh the same, then the heavier one is obviously the poisonous pill.