You have a GPS that takes 2 working batteries. You have 8 batteries but only 4 of them work.

What is the fewest number of pairs you need to test to guarantee you can get the GPS on.

# Interview Puzzles

## Collection of Puzzles asked in Interviews

This section of the website has been made to help the guys prepare for jobs/interviews and of course for those who like brain teasers. First try to solve the puzzle on your own, then look for solution. Each problem is a challenge in itself, so give them your best try.

### Crack these crack the interview

## Hour glass problem

You are given two hour glass which can measure 4 and 7 min respectively. now you have to calculate 9 min using these two hour glass (Note: you have to calculate it at a stretch)

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## Bar with 25 seats

There is a bar with 25 seats in a line. The people there are anti-social so when they walk in the bar, they always try to find a seat farthest away from others. If one person walks in and find there is no seat are adjacent to nobody, that person will walk away. The bar owner wants as many people as possible. The owner can tell the first customer where to sit. all the other customers will pick the farthest possible seat from others.

**So where should the first customer sit?**

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## What did the peasant said?

A peasant is convicted in China. He gets the death penalty. The judge allows him to say a last sentence in order to determine the way the penalty will be carried out. If the peasant lies, he will be hanged, if he speaks the truth he will be beheaded.

The peasant speaks a last sentence and to everybody surprise some minutes later he is set free because the judge cannot determine his penalty.

What did the peasant said?

## Paradox Dragons

I met three dragons. One always tells the truth, other one always lies and the last one alternates between lie and truth.

**Dragon 1:** You may ask us one question, then you must guess which dragon is which

**Dragon 2:** He’s lying. You may get three questions

**Dragon 3:** Oh no. It’s definitely one question

I asked the first dragon a question

**Me:** What would the second dragon say if I were to ask it if the 3rd dragon had been lying when it agreed with the first one that I could ask only one question

**Dragon 1:** He’d say, “Yes, the 3rd dragon was lying”

Then I asked a second question addressing the three dragons…… But they remained silent.

And, I solved the puzzle in 90 sec.

**So, which dragon is which?**

## 100 floors with 2 eggs puzzle

There is a building of 100 floors If an egg drops from the Nth floor or above it will break. If it’s dropped from any floor below, it will not break. You’re given 2 eggs. **Find N**, while minimizing the number of drops for the worst case.

## Genie with c hats

A bunch of men are on an island, A genie comes down and gathers everyone together and places a magical hat on some people’s heads (i e , at least one person has a hat). The hat is magical: it can be seen by other people, but not by the wearer of the hat himself. To remove the hat, those (and only those who have a hat) must dunk themselves underwater at exactly midnight. If there are n people and c hats, how long does it take the men to remove the hats? The men cannot tell each other (in any way) that they have a hat.

**Note:** Genie does not tell how many hats she has put.

Check your answer:-

## Cook the egg for 15 minutes puzzle

You are trying to cook an egg for exactly fifteen minutes, but instead of a timer, you are given two ropes which burn for exactly 1 hour each. The ropes, however, are of uneven densities – i e , half the rope length-wise might take only two minutes to burn. How can you cook the egg for exactly fifteen minutes?

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## Find celebrity in the party

There are (n+1) people in a party, they might or might not know each others names.

There is one celebrity in the group(total n +1 people), celebrity does not know any of n peoples by name and all n people know celebrity by name.

You are given the list of people’s names(n+1), You can ask only one question from the people. **Do you know this name ?**

**How many maximum number of questions you need to ask to know the celebrity name?**

**Note:** assume all names are unique. and you know the persons by name(but don’t know if he is celebrity)

## 100 people with sword puzzle

100 people standing in a circle in an order 1 to 100. No.1 has a sword. He kills next person (i.e. no. 2) and gives sword to next to next (i.e no.3). All person does the same until only 1 survives. **Which number survives at the last?**

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