There are a lot a weights and weighing puzzles around, but we think we've found an unusual one.
You have ten sets of ten weights. With one of the sets of weights there was a manufacturing error, and each weight in the set was made ten grams overweight. This means that the set in question is 100 grams overweight in total.
Unfortunately you don't know which is the faulty set, and visually there is no way to determine if a weight is heavier than its counterpart from another set. But you do need to find the faulty set of weights.
Fortunately you have an accurate weighing machine available.
How can you find out which is the faulty set of weights in one weighing?
Select one weight from set one, two weights from set two, and so on. Work out what the total weight should be, and then weight them all.
If the weighing comes out ten grams overweight then the faulty set is set one. If it's 20 grams overweight it's set two that is faulty. And so on.