Montu poses a puzzle to his friends: 3 balls look similar in size. One of them is heavier and 2 balls are equal in weight. You have only a pan-balance and no weights. Using the 3 balls and the pan-balance, can you identify which is the heavy ball?
How many times will you have to weigh?
Only one time. By placing one ball on each side of the balance, we can identify the heavy ball in a single weighing.
Use the balance only one time and tell which is the heavy ball.
Place any two balls on the balance. If they balance, the third ball is heavy. If they don't balance, the heavier side has the heavy ball.
Explanation
(a) The puzzle can be solved in just one weighing by comparing any two balls. (b) This method guarantees finding the heavy ball in one weighing by using logical deduction.