A problem by Luísa Quintão
There are ten piles of ten bricks each. Nine of the ten piles have each of their bricks weighing 1kg and the pile left has each of its bricks weighing 1.1kg. Considering you have one weighing-machine, what is the minimum of times you would have to use it to find out which pile has the 1.1kg bricks?
PS; you can't put all the piles/bricks on the weighing-machine and take them out one by one or anything like that; you can't gradually add one pile/brick after another or anything like that
The answer is 1.
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1 solution
Take 1 brick from pile number one, 2 bricks from pile number two, 3 bricks from pile number three and so on. You're gonna have a total of 55 bricks (1+2+3+4+5+6+7+8+9+10). If the first pile is the one with the 1.1kg bricks, the weight will be 55.1kg. If it's the pile number two, there will be a weight of 55.2kg and so on