Originally Posted by norway1456
Imagine yourself as the detective in a forgery case. Laying in a row before you are 11 coins. You know that three of them are false and 8 are genuine. You also know that the three forged coins are laying together, side by side, somewhere in the row. The false coins are heavier than the genuine one. How many coins (at a minimum) do you have to weigh before you can point out the three false coins.
Four coins in just two weighings.