What are some of the puzzles asked in an interview?

Puzzles are asked to assess how quickly you can think on your feet and how you might approach complex problems. If you are attending interview for analyst profiles, you must practice solving basic puzzles.

1. Bag of coins

You have 10 bags full of coin. There are infinite coins in each bag. But one bag has fake coins. Each coin weighs 1 gram but fake coins weigh 1.1 gram each. In how many turns can you identify the fake bag with the help of a digital weighing machine?

Answer: 1 turn

Take 1 coin from 1st bag, 2 coins from 2nd bag, 3 coins from 3rd bag and so on … similarly 10 coins from 10th bag.

Weigh all 55 (1+2+…+9+10) coins.

If the reading ends with 0.2 then the 2nd bag is fake, if it ends with 0.8 then 8th bag is fake.



2. Divide in 2 children

You have a glass of Juice. How will you divide the juice into 2 children so that both feel- they got equal share of juice. You have one empty glass of different shape and size.

Answer: Ask one of them to divide the juice into 2 equal parts. Then ask the other one to choose his glass. Now both should be satisfied.

3. Monty Hall Puzzle

You are playing a game show. You have been given 3 doors. Behind 2 doors, there are goats and 1 door has car behind it.

If you have chosen a door, the host will open the other door which has a goat behind it. And then the host asks you to choose the door with the car. Should you change the choice?

Answer: Yes

If you switch, the probability of getting the car will be higher i.e. 66%.
If you stick to your choice, the probability will be 33%.



4. Clock angle

What is the angle between the minute hand and the hour hand of a watch when the time is 3:15 PM.

Answer: You will say zero but it isn’t.

When the minute hand shows 15 minutes, the hour hand will pass ahead.
So the angle will not be zero.

In 12 hours the hour hand completes 360 degree
so in 3 hours 15 minutes i.e. 3.25 hours, it will complete (360/12)*3.25 = 97.5 degree

In 60 minutes the minute hands completes 360 degree
So in 15 minutes, it will complete (360/60)*15= 90 degree

Hence the angle between minute hand and hour hand will be 97.5-90= 7.5 degree.

5. Pizza problem

Which is larger- 2 small size pizza or 1 medium size pizza?
Consider equal thickness of both but the radius of medium pizza is twice the radius of smaller one.

Answer: One medium pizza is 4 times larger than 1 small pizza.

Suppose radii are 3 inch and 6 inch respectively.
Area of 2 smaller pizza= 2*(pi*3*3) = 18 pie inches
Area of 1 medium pizza = pi*6*6 = 36 pie inches

Here is how to approach puzzles.

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