puzzle

Billiard Balls
You have 8 billiard balls.Seven weigh exactly the same; one is heavier.You also have a balancing scale.How can you find the heavy ball in only 2 weighings?

Solution
If you have not thought for atleast some time before resorting to find the solution below, you may not understand the solution below.

These questions has to be attacked through negative / elimination thinking.

To find the heavy ball, the final weigh should be with 2 balls. If they are in equilibrium, then you can have a third ball kept outside and consider it heavier.

So the pick is three balls on each side in the previous weighing. so weigh three balls each side on the previous move. if they are in equilibrium, pick up the rest two and weigh them and you know which one is that.

If they are not in equilibrium, pick up the heavier lot of 3 and weigh with one ball on each pan and keep one ball out of pan, if the balance is in equilibrium, then the third ball is heavier, else the balance shows the heavier ball.