Play · Tricky
Ten bags, one fake
Ten bags of coins. Real coins weigh 10 g. One bag is full of fakes that weigh 9 g. You have a digital scale and can use it once.
The puzzle
Choose how many coins to take from each bag, then weigh them all together.
— gdigital scale
How to think about it
Find a hidden signal
One weighing gives you one number, so make that number name the bag. Take a different number of coins from each bag: 1 from bag 1, 2 from bag 2, and so on. Each fake coin is 1 g light, so the grams missing tell you which bag the fakes came from.