You have ten identical open-topped boxes with 10 visually identical coins
In nine of the boxes each of the 10 coins has a mass
In one box the 10 coins have masses of only 9g each.
How can you find which box is the odd one out?
You have a normal mass measurer with a single pan and a scale. With just
one weighing you can identify the box with the lighter coins.
What will you weigh?