8 identical balls are placed side by side with 7 balls of same weight and one of lower weight. you are given a pair of weighing scales just like these vegetable vendors. how can you find out the lightest ball??
Answers
Let us number the balls from 1 to 8
Now make groups
Ball group A = {1,2,3}
Ball group B = {4,5,6}
Ball group C = {7,8}
Now weigh group A and B on weighing scale. If the lighter ball is in one of the two group you will know. Then suppose lighter ball is in group A, so take ball 1 and 2 and weight them, if any of them is lighter then it will weigh less on weighing scale but if not then you will know ball 3 is the lighter ball.
If the lighter ball is in group B then weigh ball 4 and 5 if any of them is lighter then it will weigh less on weighing scale and if none of them is lighter then ball 6 is the light weight ball.
But when in the start we weighed group A and B and suppose none have the lighter ball then we are sure that lighter ball is in group C. Accordingly you can weigh ball 7 and 8 and you will get the lighter ball.