I have three blocks. Two of them are the same weight. The third is a different but unknown weight (it could be heavier or lighter).
Using a balance scale at most two times find the odd block.
Label them A B and C.
Compare A and B, then A and C , and you will identify the
faulty block, and also find out whether it is overweight or underweight.
However we were asked to find the odd block and not necessarily to decide whether it is over- or underweight.
If only identification is required - 2 uses od balance scale will take care of
The same procedure (Compare A and B, then A and C) can be
applied, but there might be a case non existing previously: iff A = B, and A=C, D is the bad guy, but we
do not know whether it is heavier or lighter than the others.
So we got solutions for two cases : 1 out of 3 and 1 out of 4, using exactly the same procedure.
1st case- always provides the odd one and information.
2nd - always picks up the odd block and sometimes provides the info (over or under).