Which company is faulty?Level pending
There are 9 bags of balls of 9 different companies. If all of the companies make identical (in each aspect) balls, each weighing 20 units, but 1 of the company makes faulty balls of lesser weight, and you have as many balls as you want of each company, and a weighing machine. A "weighing of the balls" refers to measuring the total weight of any combination of balls from the companies. What is the minimum number of weighings that are needed to determine the faulty company?