Home Interview tips 10 Common Puzzles Asked in Freshers Interview

10 Common Puzzles Asked in Freshers Interview

April 26, 2018

131189

Puzzle Solving is a common technique used by recruiters during freshers interview to hire for analytical roles and roles that require plenty use of logical reasoning. Several companies still adopt this method for assessing candidates for their organization which makes it imperative to be prepared for.

We, thus, have compiled a list of ten common interview puzzles to help you in your fresher job interview.

Puzzle 1 – Find the faulty coin

You have ten stacks of ten coins each and each of them weighs 10 gm. However, one of the stacks is faulty and each of the coins in it weighs only 9 gms. What is the least number of times you have to weigh to find the faulty coin?

Solution

Yup 10 would be ideal but not the least. The least number of times you have to weigh is just once! Line up the stacks and pick 1 coin from first stack, 2 coins from second stack, 3 coins from third stack and so on. You will have a total of 55 coins. Now weigh it. If all of them were the right weight, the total would be 550 gms. If the total is 549, the first stack is faulty; if the total is 548 then the second stack is faulty and so on.

Puzzle 2 – Measuring 45 minutes with two identical wires

You have two identical length wires which take an hour to burn. But, they don’t burn at the same speed. How do you measure 45 minutes based on the burning?

Solution

You first light up three ends of the two wires. The remaining end you can light up once the first wire is completely burnt. When the second wire is completely burnt, the time is 45 minutes.

Puzzle 3 – Find the age of sons

Arun has three sons and his friend Shakti wants to know their ages. Arun gives him three hints as Shakti couldn’t answer till the third hint –

The product of their ages is 72
The sum of their ages is the same as my house number
The oldest of sons love chocolate icecream

Solution

First, you will get 12 possibilities for the equation XxYxZ = 72. Next, the sum of each of the numbers is added. You get a variety of numbers but there are two possibilities where the sum is 14. 2+6+6 and 3+3+8. Arun mentioned that his oldest like chocolate icecream, which meant there is only one older child and hence, the sons ages are 3,3 and 8.

Puzzle 4- Calculating pay using 7 units gold rod

A contract employee needs to be paid everyday but the employer has only one rod of 7 units of gold. He can make only at max 2 cuts. How does he manage to pay him?

Solution

The employer makes two cuts so that he has units of 1, 2 and 4.

Day 1, the employer gives him 1 unit. On day 2, the employer takes back the 1 unit and gives him 2. On day 3, he gives him 1 unit. On day 4, he takes back the 1 and 2 units and gives him a 4 unit. So on until day 7 when he gives him all the units.

Puzzle 5 – Switching on the right bulb

This is one of the most common puzzles for interviews.

You have a room behind a door and there are three bulbs inside the room. You can find its three switches outside the door. You can switch them on and off as many times as you wish but once you open the door you cannot change them. Identify which switch is connected to which bulb.

Solution

Let the lightbulbs be X, Y and Z. Switch on and off X for 5 to 10 times. Now immediately switch off X and switch on Y and open the door. The lightbulb which is on is Y. The lightbulb which is hot but off is X. The lightbulb which is off and cold is Z.

Puzzle 6 – Increase the probability of the white ball

You have two bowls which will hold 50 balls each. Now you have 50 black balls and 50 white balls and you cannot place all balls of same color in each bowl. Now you have to pick a random ball from a random bowl. How do you maximize the probability of getting a white ball?

Solution

You place 49 white balls in one bowl and 1 white ball in the other mixed with all the balls. The probability of picking the white ball is ½*1+ ½*49/99 which is approximately ¾.

Puzzle 7 – Find the colour of the last ball

You have bag with 20 blue and 13 red balls. Your task is to pick two balls in succession. If the balls are the same colour then you remove them and replace them with a blue ball. If the balls are of different colour then you remove them and replace them with a red ball. What is the colour of the last ball?

Solution

The last ball will be red. The puzzle is about odds and evens. For instance you pick a red and blue ball, you will place red ball back inside. The red balls will always be in odd numbers. Hence, the last one will be a red ball.

Puzzle 8 – Placing coconuts in a line

Your task is to place 10 coconuts in 5 lines such that each line has 4 coconuts.

Solution

You have to place them in a star shape with the centre being a pentagon. Each coconut will be placed at the intersection and meeting point of 2 lines.

Puzzle 9 – Who’s married and who’s not?

Three people are in a room. Rahul looks at Nisha. Nisha looks at Sahil. Rahul is married but Sahil is not married. At any point, is a married person looking at an unmarried person? Yes, No or Cannot be determined.

Solution

Yes, at every point there is a married person looking at an unmarried person. The only person whose information we don’t know is Nisha. Assume Nisha is married, she is looking at Sahil. So, married person is looking at unmarried person. Now assume Nisha is unmarried, Rahul is looking at Nisha. So even then married person is looking at an unmarried person.

Puzzle 10 – Which way will the ants go?

Three ants are located on an equilateral triangle. Now each ant picks a random direction and starts to move along the triangle. What is the probability that they don’t collide?

Solution

0.25. This is because the ants will not collide only if they all move in the same direction. Now, each ant has two choices, to move either side – clock wise or anti-clockwise. Hence,

P(No collision) = P(All ants go in clockwise direction) + P(All ants go in anti-clockwise direction)

P = 0.5*0.5*0.5 + 0.5*0.5*0.5 = 0.25

So those were some of the most common puzzles that are asked in fresher interview. They are all based on simple mathematical logic, so be prepared with your permutations, combinations and probability. Also, the same puzzles are often asked with different objects or names, but the logic is always the same. So fret not!

A few very important and helpful tips for you on how to answer these puzzles in the freshers interview –

Listen to the puzzle properly, and preferably ask for a notepad to write down the main points
Avoid asking the question again and again, and instead, refer to the notes
Stay calm; while the recruiters are looking for an answer, they are often looking at how you are approaching the puzzle
There is no time limit or a stopwatch hanging over your head but at the same time don’t linger too much with thinking, start thinking loud so the panel knows what you are thinking
Even if you can’t get the answer, offer the best possible scenario
Under no circumstances should you panic! Don’t show signs of stress or worry

Puzzle interview questions stand out as it helps the recruiter access how smart you are and how well you can think off your feet. Sometimes, there are no right or wrong answers to these puzzles but how you approach the question matter a lot.