You are given 8 balls that look alike. All are of same weight except for one that is lighter by a kilo.You are given a balance and 2 chances to separate out the lightest.
Answer: Divide 8 ball into 3 groups. 2 groups of 3 balls and one group of 2 balls. First take the 2 groups of 3 balls and place one group on the left and other to the right.
Case 1- One side of the pan containing lighter ball goes up:
That means one of the 3 balls is lighter. Clean the balance and take any 2 balls from the lighter group and place them on either side of the pan. If this weighing contains any lighter ball then that side of the pan goes up. If both balance out to be equal, than the lighter ball is the one that is left out.
Case2 -Both balance out to be equal:
This implies that the lighter ball is one among the 2 left behind. Clear the balance and place one ball on each side and weigh them.
The same thing can also be applied for 9 balls where each group will have 3 balls.
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