You are given a task of locating one faulty coin out of 99 identical in appearance coins i.e. 98 of equal weight and one of a lesser weight; and to achieve it within seven weighings, using a balance scale.

Sounds familiar and easy (3⁷>99)?

Familiar? Yes.

Easy? Not quite!

How can you accomplish it if no coin may be weighed more than twice ?

Bonus task: After devising the requested procedure please generalize:
How many coins (n-1 normal and one lighter) can be resolved within k weighings?

Should be  

 97  identical in appearance coins i.e. 96 of equal weight and one of a lesser weight;

Then it is fully solvable (worst choice included).

If anyone can correct the puzzle  - please do so ASAP.

Edited on July 2, 2014, 2:37 am

Posted by Ady TZIDON on 2014-06-01 16:03:33