Dangerous Interview Puzzles

Even if you have become Pro in Excel and SAS, one thing that will keep haunting you mostly during an interview are logical puzzles. These puzzles are asked to you to test your logical and analytical thinking and would keep haunting you for quite a long span of your career.

Let us look at some very frequently asked puzzles asked during interviews.


Lighting Bulb Puzzle

A light bulb is hanging in a room; Outside of the room, there are three switches, of which only one is connected to the bulb. In the starting situation, all switches are off' and the bulb is not lit . If it is allowed to check in the room only once to see if the bulb is lit or not (this is not visible from the outside), how can you determine with which of the three switches the light bulb can be switched on?


I think this is one of the most loved puzzles of many interviewers and this makes it a "Popular Puzzle".

Solution:  We will first switch on the first switch button and let it remain ON for 5-6 mins. After waiting for 5-6 mins we will switch it off. Then we will switch on the second switch button and will go the room to see if the bulb is lighted or not. If the bulb is lit then off course it is this second bulb, if not we will touch the bulb and see if it is hot or not, if hot we can assume that the it was the first switch that lit the bulb, since we kept the bulb switched on for 5-6 mins.IF not any of these then of course it is the third switch.

voilà, you solved it !


Blind man and the island

A blind man is alone on a deserted island. He has two blue pills and two red pills. He must take exactly one red pill and one blue pill or he will die. How does he do it?


This is kind exactly a puzzle but a riddle. There are many possible answers to this riddle but I shall explain the solution that according to me is the best. I would appreciate if the Ask Analytics readers send other solutions according to them that they think are appropriate.

                                                    Solution:  The blind man can expose his pills to the sunlight and feel a noticeable difference in the temperature because of the amount of heat absorbed by each pill. 
       The red pill will become hotter than the blue pill since it will absorb more heat and thus he will be able to differentiate between the two colors.

As, I told you there are "N" number of different ways to answer this puzzle but this is one of them, appreciate other answers too.



People crossing the bridge Puzzle

Four people need to cross a rickety bridge at night. Unfortunately, they have only one torch and the bridge is too dangerous to cross without torch. The bridge is only strong enough to support two people at a time. Not all people take the same time to cross the bridge. Times for each person:  1 min, 2 mins, 7 mins and 10 mins. What is the shortest time needed for all four of them to cross the bridge?

This puzzle was recently asked in an interview I attended, and I really had fun solving it. 

                                                           Solution :   A = 1 min
                                                                              B=  2 min
                                                                              C = 5 min
                                                                              D = 10 min                                                          
  • A and B cross together =2 mins 
  • A comes back =1 min 
  • C and D cross together = 10 mins
  • B cross the bridge = 2 mins
  • A and B cross  together = 2 mins                                                 

Total Time =2+1+10+2+2=17 mins

Weighing Puzzle


There are 9 balls with equal size, but 1 ball has more weight than the rest of the balls. We have 1 scale. How would you find that ball that has the extra weight if in the process you have to use the scale the minimum amount of weighs possible?


SolutionThis is a very cliche but one of the most interesting puzzles asked during interviews. Let us try and understand how to go about this puzzle step by step.

Step 1-Divide the balls in 3 groups(of 3 balls each)
Step 2- Weigh any two groups on the weighing scale.
Step 3-If either of the groups is heavy, select that group of balls. And if both are equal, select the 'third group' (which was not selected in Step 2)
Step 4- Randomly select any two balls from the selected group (chosen in step 3) and weigh them.
Step 5- If any of the balls are heavy, that is your ball. If both are equal, the un-selected ball of that group is yours.


So, in order to find that ball which weighs heavier you ideally have to use the scale just TWICE.

Mis-labelled Jar Puzzle

The first box has two white balls. The second box has two black balls. The third box has a white and a black ball. Boxes are labeled but all labels are wrong! You are allowed to open one box, pick one ball at random, see its color and put it back into the box, without seeing the color of the other ball. How     many such operations are necessary to correctly label boxes?


Solution :  Just one. How? Let us find out.
                    
 Because we know all labels are wrong.So the BW box must be either BB or WW. Selecting one ball from BW will let you know which one it should really been labelled as ( since all the labels are wrong). And the other two boxes can then be worked out logically, Ask Analytics readers are enough smart for that.

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