# Coin weighing puzzle

We have 5 boxes with 20 coins each. And coins of three boxes weigh 10, one of them weighs 9 and the other weighs 11. How can we differentiate between them by using a scale(digital, not the one with two cups) only once, with 1 unit accuracy?

• Weigh them? shrugs This puzzle needs more restrictions to be meaningful. – mr23ceec Dec 11 '17 at 16:14
• @mr23ceec "using a scale only once" – Apep Dec 11 '17 at 16:15
• Is it a balancing scale (two cups and one side is equal to the other) or a spring scale (one cup and it gives you a numerical answer, usually in a certain range) – mr23ceec Dec 11 '17 at 16:23
• One cup digital scale – Nemexia Dec 11 '17 at 17:11
• each coin weigh 10 or whole box weigh 10? – Oray Dec 11 '17 at 18:07

This is pretty straight forward question. Just choose $0,1,3,7,12$ and this is also the minimum number of coins you can choose as well. You will get different $20$ results except the boxes with coins with the same weight coin.