Mostly asked weighing balls puzzles in interview

I have faced many interviews ,got through many rounds. I m sharing my experience. Mostly in hr rounds, interviewer asks puzzles to play with student mind. I can say that clearing tech round or aptitude round is simple. Bt puzzles r very difficult to solve. Your mind doesn't perform well when someone unexpected questions. Literally, if you have some previous experience how to solve puzzles.Then it becomes easier for solving puzzles. Weighing puzzles is most likely asked in the interview.


1) we have 9 identical balls bt 1 heavy weight. We have to find that ball in minimum no. of weighing. Remember this is understandable only one pan with two halves to measure.

divide into 3 group with 3 balls each

This is basic step always divide balls in equal balls if possible. So 9balls/3=3balls (in each group)

So now put 3 balls in two pans. Suppose they r equal. Now you left with 3 balls.Put 1 ball in one side and 1 ball in other side. If they r equal. The ball which left is culprit or heavy weight ball.

Now suppose while weighing 3 balls in each side. We got one side heavy. Now take out all three balls from heavy side. Measure balls with 1 ball at each side. If we get it then it's fine otherwise left ball is heavy one.

So minimum we can get heavy weight ball in 3 trials.

 
2) Suppose we have 8 balls now find out heavy ball in those.

Now this is different case. We can't divide equal balls in groups. Firstly think before giving answer its very difficult in the beginning.

Make group like that for minimum no. of iterations.

2 group = 3 balls
1 group = 2 balls

Put 3 balls in one side and 3 balls in other. If both r equal. Then check 1 ball with other ball.


3) 12 balls in which one ball either heavy or light. You know minimum 3 iteration needed to find that ball. How could you do it?

Divide balls into 3 groups

12 balls/3 balls= 4 balls in each (maximize no. of  balls)

Weigh 2 groups 4 balls each in two sides. Now we left with 4 balls. Weight this group with any previously measured group. Then find out its complicated. I will tell you the correct solution. Before that go for the how to solve.


These r the puzzles which most likely to ask in HR interview or puzzle round. Don't think its too difficult to answer. Only need is right technique and approach.