Gold Coins

Logic Level 3

You have 10 identical bags containing 10 gold coins each. All of the coins weigh 10 grams, except for the coins in one of the bags which instead weigh 9 grams.

If you have a scale which tells you the total weight of whatever you place on it, then how many weighings are required to determine the bag whose coins are lighter?

Note: You can separate coins from their bag, and you can assume the bags have negligible weight.

Excel in math and science

Master concepts by solving fun, challenging problems.

It's hard to learn from lectures and videos

Learn more effectively through short, conceptual quizzes.

Our wiki is made for math and science

Master advanced concepts through explanations, examples, and problems from the community.

Used and loved by 4 million people

Learn from a vibrant community of students and enthusiasts, including olympiad champions, researchers, and professionals.