VERSION 2!!!
Weigh coins 1 2 3 on the left and 4 5 6 on the right. Leave 7 and 8 at one side first.
Since the counterfeit coin is lighter, the weighing scale on either side will go up.
If the one on the left goes up, either of coins 1 2 3 is the counterfeit coin.
weigh coin 1 on the left and coin 2 on the right.
If it balances, it means that coin 3 is the counterfeit coin.
If one of the side goes up, the one that goes up is the counterfeit coin.
If the weighing scale balance, it means that either of coin 7 or 8 is the counterfeit coin.
weigh coin 7 and 8 on each side, the one that goes up is the counterfeit coin.
