There’s also another answer to this Puzzler:

Divide the 50 coins into three piles of 21, 21 and 8. Weigh the two piles of 21 [WEIGHING 1]. If they are the same weight, set aside the two piles of 21 coins then take the pile of 8 coins and divide it in half. Weigh each pile of 4 coins [WEIGHING 2]. Split the heavier pile of 4 coins into two piles of two coins and weigh them [WEIGHING 3]. Take the heavier pile of two coins and split it into separate coins and weigh them [WEIGHING 4]. The heavier coin is the one we’re looking for.

If one of the piles of 21 coins is heavier than the other, discard the lighter one and split the heavier one into three piles of 7 coins each. Weigh two of the piles [WEIGHING 2]. If the piles have the same weight, discard them and work on the third pile. If one of the piles of 7 coins is heavier than the other, use the heavier one. No matter what, now you’re working with a pile of 7 coins.

Divide the 7 coins into groups of 3, 3 and 1. Weigh the two groups of 3 coins [WEIGHING 3]. If these two groups of coins weigh the same, the coin we’re looking for is the lone coin left out. If one of the groups of 3 coins is heavier than the other, take the heavier one and divide it into individual coins. Weigh two of the coins [WEIGHING 4]. If the coins weigh the same, the lone coin left out is the one we’re looking for. If one of the coins is heavier than the other, the heavier coin is the one we’re looking for.