Logical Reasoning Questions and Puzzles form an important part of an interview process. These are aimed towards checking aptitude and logical problem solving skills of an interviewee. In most of the cases, interviewers usually don’t worry too much about the final answer, but what is really looked at is the approach you take to solve a problem. Hence, it’s important to explain your approach and thought process to an interviewer. In this section, we have tried to list down and cover different types of puzzles through limited number of questions that can give you a good background and flair of puzzles asked. To highlight the approach taken to solve these puzzles, we have provided detailed explanations in the answers. 10 of them are placed heads up and 90 are placed tails up. You can’t feel, see or in any other way find out which side is up. Now, split the coins into two piles such that there are equal numbers of heads up in each pile. Make two piles of the coins. Put 10 coins in one pile and 90 coins in another. Now, both the piles have equal number of heads up. You are given eight identical looking balls. You are provided with a simple mechanical balance to weigh the ball. Two trials will be needed. Divide the balls in three groups. Both sides are equal. Both sides are not equal. Again, if both the sides are equal, you know that 3rd ball in the same group is heavier. Else, you would be able to see heavier ball from the balance. Prisoner W is standing on one side of a wall, and prisoners X Y and Z are standing on the other side of the wall. W || X Y Z Where, the || represents a wall. The wall has no mirrors. So, prisoner W can see the wall and nothing else. There are 2 white hats and 2 black hats and each prisoner has a hat on his head. Each prisoner cannot see the color of his own hat, and cannot remove the hat from his own head. But the prisoners do know that there are 2 white hats and 2 black hats amongst themselves. The prison guard says that if one of the prisoners can correctly guess the color of his hat then the prisoners will be set free and released. Note that the prisoners are not allowed to signal to each other, nor speak to each other to give each other hints. But, they can all hear each other if one of them tries to answer the question. Also, you can assume that every prisoner thinks logically and knows that the other prisoners think logically as well. Now, if X doesn’t answer the question for some time, Y would infer that since X is not able to answer the question, Y and Z must be having hats of different color on their heads. Hence, Y would be able to answer the question after looking at color of hat on Z’s head. If Z has a white hat on his head, Y would answer black, else white. There are five persons. Out of these five, only one is the truth teller and the remaining four are togglers i.e. But on being asked again, they will switch i.e. You need to ask only two questions to determine who the truth teller is. You can ask both the questions from the same person or ask one question each from two different people. How will you determine who is the truth teller? Are you the truth teller?. If the response to this question is Yes, then that person can be either a truth teller or a toggler who is lying. Who is the truth teller? If the picked person is the truth teller, his response to second question would be I am the truth teller. Otherwise, if the picked person is a toggler who lied to first question, he would have to tell truth for the second question and point to the truth teller. Else if the response to first question is No, then that person is a toggler who is telling the truth. Now, since the toggler has told the truth once, he would lie to second question. Who is not the truth teller?, and you will find out the truth teller. There are 100 prisoners in 100 different prisons. There is a bulb in each prison which is controlled by a switch outside that prison. Initially bulbs in the all the prisons are glowing. Would toggle in first iteration only. Hence, we see that out of first ten prisons, only prison 1, 4 and 9 would have bulb switched off after 100 iterations. This gives hint that squares of a number are the ones with off multiples and hence we can extend this logic. Which bulb will glow brighter and why? The bulbs are in series so the amount of current flowing through each is same. One door leads to heaven and the other door leads to hell. One guard always tells the truth and the other guard always lie, but you don’t know which one is honest and which one is liar. Given that you can only ask one question from one of them, what would your question be in order to find the way to heaven? ’ If I ask the other Guard about which door leads to heaven, what would he tell me? The door that the Guard specifies will lead to hell. Other door would lead to heaven. This is due to the fact that if you end up asking this question from the Guard who always tells the truth, he would point you to the door that leads to hell as he knows that the other guard would lie and would point you to the door that leads to hell. On the other hand, if you end up asking this question from the Guard who always lies, he would lie and point you to door to hell. You have one person working for you for exactly seven days. You have a gold bar to pay him. The gold bar is segmented into seven connected pieces. You must give the person a piece of gold at the end of every day. You can make only two cuts to the gold bar. Where would be these two cuts to allow you to pay the worker 1/7th gold bar each day? It’s dangerous to cross the bridge without a touch. The bridge can support only two people at a time. What is the shortest time required for all four of them to cross the bridge? F13, S15, T17, T19, S21, M23, __? Monday 23rd Next date in the series would be 25th and day would be Wednesday. Hence, the answer would be W25 . Two hundred people line up to board a plane with 200 seats. If Jack sits on his seat, Jill would find her seat unoccupied and if Jack sits on Jill’s seat, Jill would find her seat occupied. Let us now consider all 200 seats. Let’s assume Jack sits on the seat belonging to 35th person in the line. Persons 2 to 34 will sit on their own seats, and when person 35 comes in, he can sit either on the seat belonging to Jack or some random seat. If person 35th sits on Jack’s seat, Jill will find her seat. Two old friends, A and B, meet after a long time. I got married and now I have three kids. How old are your kids? Product of their ages is 72 and the sum of their ages is the same as your birth date. But I still don’t know. My eldest kid just started taking piano lessons. How old are Bill’s kids? Now, as A is not able to find their age from this data, it means that there are two or more sets with same sum. There is a triangle and on it are 3 ants, one on each corner, and they are free to move along the sides of the triangle. What is probability that the ants will collide? It is given that ants can move only along the sides of the triangle in any direction.