In a group of 80 coins, exactly one is counterfeit and weighs less than the others. U are provided a scale to weigh to coins. The min. no. of weightings req. to determine the counterfeit coin is

a) 4 b) 1 c) 5 d) none of these

• a)4
  27 27 26
  9 9 9
  3 3 3
  1 1 1
• 13 years agoHelpfull: Yes(3) No(9)
• 1st divide 80 coins in 2 groups,each having 40 coins.compare their weight take the lighter group(having 40 coins)
  divide 40 coinns in 2 groups.similar after coparing their weight take the lighter group(having 20 coins)
  divide it in 2 goups,take lighter group(having 10 coins)
  divide it in 2 groups,take lighter group(having 5 coins)
  divide into 3 groups,2 groups of 2 coins,and 1 single coin.
  2 possibilities.
  1.2 group of coins is of similar weight then,the lighter coin is the single coin.
  2. if 1 of thos group is lighter than other take that group,and again divide it into 2 groups(each having 1),compare their weight,u will get the lighter 1
  
  for the 1st possibility 5 comparisons is required,but for the 2nd possibility 6 comparisons required
• 10 years agoHelpfull: Yes(3) No(0)