**"Probability"**

## Dice game – 7 or 12?

*By admin On April 8, 2012 · 5 Comments*

Two people, ‘A’ and ‘B’ play a game of dice. 2 dices are continuously being thrown on the table. ‘A’ wins if 12 shows up, ‘B’ wins if two 7′s come up in consecutive throws. Game ends whenever there is a winner. What is the probability that ‘A’ wins?

Every person in this world (assume 7 billion people) has a fair coin except one. One person has a coin which has heads on both sides. A random person is chosen who flips his/her coin 100 times. If it comes out to be heads each time, what is the probability that the person has a fair coin?

## How many sons?

*By admin On July 23, 2010 · 9 Comments*

A man has two children. He says one of them is a son. What is the probability that the other one is also a son?

## Crazy man in the airplane!

*By admin On February 2, 2010 · 2 Comments*

A line of 100 airline passengers is waiting to board a plane. they each hold a ticket to one of the 100 seats on that flight. (for convenience, let’s say that the nth passenger in line has a ticket for the seat number n.)

Unfortunately, the first person in line is crazy, and will ignore the seat number on their ticket, picking a random seat to occupy. all of the other passengers are quite normal, and will go to their proper seat unless it is already occupied. if it is occupied, they will then find a free seat to sit in, at random.

What is the probability that the last (100th) person to board the plane will sit in his proper seat (#100)?

7 thieves wanted to lock the treasure looted from a ship. They wanted to put N no. of locks to the treasure where each lock had multiple keys. Find the minimum number of locks N and minimum no. of keys K with every thief subject to the following conditions:-

All the locks should open each time a majority of thieves(4 or more) try to open the locks.

At least one lock remains unopened if less than 4 thieves try opening them.

All locks should have same no. of keys.

All thieves must have same no. of keys with them.

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