Posted by alya on .
you have 6 iron balls. 5 iron balls have equal weight and 1 iron ball is slightly lighter than the other 5 iron balls. you are given a libra. find ways (most minimum) to find out the light.

PROBLEM SOLVING IN MATHEMATICS 
Reiny,
typically in this type of question, you can only use a "fair balance"
1st weighing:
place 3 balls on each side of the balance, that will tell you which set of 3 contains the lighter ball
2nd weighing:
place a ball on each side of the balance, keep the third back in your hand.
a) If they balance, the the ball in your hand is the lightest
b) If the balls don't balance, it will show which is the lightest.
2 weighings are necessary. 
PROBLEM SOLVING IN MATHEMATICS 
Reiny,
should have said:
2nd weighing:
From the set of balls with the lighter ball, place a ball on each side of the balance, keep the third back in your hand.
etc