Puzzle solving is a common technique used by recruiters during interview to hire for analytical roles as well as roles that require use of logical reasoning.
Here are 5 puzzles commonly asked in interviews.
1.10 coins puzzle
You are given 10 coins on the table with your eyes closed. 5 coins face head and other 5 face tail. Can you make 2 piles of coins with same number of heads and tails facing up in each pile?
Don’t assume that you can differentiate heads and tails by touching coins. You can flip coins any number of times.
Make 2 piles with equal number of coins.
Now flip all the coins in any of the pile.
2.Measure 45 minutes with 2 candles
You have been given 2 candles. Each candle can burn for 60 minutes. How can you measure 45 minutes using 2 candles?
But the candles are of different shape and size. They are not even uniform.
Hint- You can light candles with both sides.
Light up first candle from both sides and the second one from one side.
The first candle will burn in 30 minutes.
Now light up the second candle from the other end, so this candle burns in 15 minutes.
3.Three boys and triangular park
There are 3 boys standing on 3 corners of a triangular park. All boys randomly pick a direction and start moving long the perimeter of the park.
What is the probability that any 2 boys collide?
Any boy has 2 choices to choose direction. So total events= 2^3 =8
The boys will not collide in only 2 cases.
So probability=2/8 = 0.25 i.e. 25%
4.Heaven and hell
There are 2 guards standing at 2 doors. One door goes to heaven and another one goes to hell. One guard always speaks the truth while the other one always tells a lie.
What question will you ask to any of the guard to find the door which goes to heaven? You can ask only one question.
Answer- Ask any guard- What would the other guard say if I ask which door leads to the hell?
Suppose you ask to the honest guard, then he will speak the truth. He knows that the other guard will lie so he will tell you the door to heaven.
In case you ask the lair guard, he will not tell correct one and eventually tell the door which leads to heaven.
5.Torch and bridge
4 persons- A, B, C & D want to cross a bridge in night. The bridge cannot be crossed without a torch. But they have only one torch.
At a time only 2 persons can cross the bridge. When two people will cross together, they move with the speed of the slower person.
A takes 1 minute to cross the bridge, B takes 2 minutes, C takes 5 minutes and D takes 8 minutes.
Answer: In 3 turns, they can cross the bridge.
1st turn- A & B go the other side in 2 minutes. A comes back in 1 minute. Total time= 3 minutes
2nd turn- C & D go the other side in 8 minutes. B comes back in 2 minutes. Total time= 10 minutes
3rd turn- A & B cross the bridge in 2 minutes.
Know how to approach puzzles in an interview.