Weighings - Find one/more bags of fake coins
I have 10 bags of 10g coins and an accurate scales.
Unfortunately, one of the bags is full of fake coins, each being 1g less than a good one.
Find, in only one measurement, which bag contains the fakes.
Same question but among the 10 bags, two bags contain fake coins.
Same question but there is one bag of 9g coins and one bag of 11g coins.
Same question but I don't now how many 9g and 11g coins bags.
Be kind : I just have 5 bags, because with 10 bags the solution is not realistic.
Why just 5 bags ?