A researcher plans to identify each participant in a certain medical experiment with a code consisting of either a single letter or a pair of distinct letters written in alphabetical order. What is the least number of letters that can be used if there are 12 participants, and each participant is to receive a different code?
Ans = B (5)
Use A, B, C,D& E as the 5 codes.
5 participants can each get one of the 5 codes.
For the remaining, use 2 code combinations from the 5 codes
10 such combinations are possible.
Hence 5 codes are suff.