Puzzle - 3

Last time I had sent you the following puzzle.

There is a virus. It multiplies to seven in an hour. There is one virus in a bottle. It takes 50 hours to fill up the bottle. How much time was taken to fill up the 1/7 (one-seventh) of the bottle? How much would it take to fill up 1/7 of the bottle if to begin with there were 7 viruses?

Its answer is 49 and 48 hours. Almost all of you sent correct answer, saying it was easy one.  
Last year during my US trip Anando (son of Ranjeet Chatterji now Ron) and Surjeet Chatterji had taken us to Grand Canyon.  Anando informed me that software and computer companies in US ask puzzles before recruitment. He informed me that this is one of the puzzles asked by them.

There are ‘n’ numbers of boxes. They contain as many balls as one can think of.  Out of these in ‘m’ boxes each balls weighs 1.1 kg. In rest of the boxes that is in ‘n minus m’ boxes balls weigh 1 kg. There is a spring balance. In how many weighing one can find the ‘m’ boxes that have balls weighing 1.1 kg. One could do it ‘n’ weighing. But that would be waste of time. What is the least number of weighing in which it can be found out? 

It is not easy as the puzzle number 2 unless you read the hints.  Try it out but if you want any hint then read on. 

Continued >----