split the coin into 26 26 26...... take any 2 26 coins..... if it is the odd coin isin remaining 26 if any one has less or more wt go for nxt and find it.. so it takes 2 trials..... 9 9 9 3 3 3 1 1 1.....
consider 2 coins no of ways 2 find the counterfeit coin is 1 consider 3 coins no of ways 2 find the counterfeit coin is also 1 since for testin u ll tak 2 coins in tat if none is counterfeit then the 3rd coin not taken for testin is counterfeit coin or in other case if a counterfeit coin is present in 2 coins tat u hav taken for testin u cud directly find out so 1test is enough for 3coins so split 80coins in terms of 3 (27 27 26) to find the counterfeit ( set) we require 1 test among de set 27 or 26 split as (9 9 9) or (9 9 8) which requires 1 test to find counterfeit ( set) among de set 9 or 8 split as (3 3 3) or(3 3 2) which requires 1 test to find counterfeit ( set) among de set 3 or 2 split as (1 1 1) or (1 1 0) which requires 1 test to find counterfeit coinnnnnnn so exactly 4 tests are required
