**Crossing the Bridge Puzzle**

**Puzzle:**

Four people need to cross a rickety bridge at night. Unfortunately, they have only one torch and the bridge is too dangerous to cross without one. The bridge is only strong enough to support two people at a time. Not all people take the same time to cross the bridge. Times for each person: 1 min, 2 mins, 7 mins and 10 mins. What is the shortest time needed for all four of them to cross the bridge?

**Answer:**

It is 17 mins.1 and 2 go first, then 1 comes back. Then 7 and 10 go and 2 comes back. Then 1 and 2 go again, it makes a total of 17 minutes.

**Burning Rope Timer:**

**Puzzle:** A man has two ropes of varying thickness (Those two ropes are not identical, they aren’t the same density nor the same length nor the same width). Each rope burns in 60 minutes. He actually wants to measure 45 mins. How can he measure 45 mins using only these two ropes.

He can’t cut the one rope in half because the ropes are non-homogeneous and he can’t be sure how long it will burn.

**Answer:**He will burn one of the rope at both the ends and the second rope at one end. After half an hour, the first one burns completely and at this point of time, he will burn the other end of the second rope so now it will take 15 mins more to completely burn. so total time is 30+15 i.e. 45mins.

**Heaven Gate Puzzle:**

**Puzzle:**

You are standing before two doors. One of the path leads to heaven and the other one leads to hell. There are two guardians, one by each door. You know one of them always tells the truth and the other always lies, but you don’t know who is the honest one and who is the liar.You can only ask one question to one of them in order to find the way to heaven. What is the question?

**Answer:**

“If I ask the other guard about which side leads to heaven, what would he answer?”.

**King and Wine Bottles**

**Puzzle:**

A bad king has a cellar of 1000 bottles of delightful and very expensive wine. A neighboring queen plots to kill the bad king and sends a servant to poison the wine. Fortunately (or say unfortunately) the bad king’s guards catch the servant after he has only poisoned one bottle. Alas, the guards don’t know which bottle but know that the poison is so strong that even if diluted 100,000 times it would still kill the king. Furthermore, it takes one month to have an effect. The bad king decides he will get some of the prisoners in his vast dungeons to drink the wine. Being a clever bad king he knows he needs to murder no more than 10 prisoners – believing he can fob off such a low death rate – and will still be able to drink the rest of the wine (999 bottles) at his anniversary party in 5 weeks time. Explain what is in mind of the king, how will he be able to do so ? (of course he has less then 1000 prisoners in his prisons)

**Answer:**

Think in terms of binary numbers. (now don’t read the solution, give a try).

Number the bottles 1 to 1000 and write the number in binary format.

bottle 1 = 0000000001 (10 digit binary)

bottle 2 = 0000000010

bottle 500 = 0111110100

bottle 1000 = 1111101000

Now take 10 prisoners and number them 1 to 10, now let prisoner 1 take a sip from every bottle that has a 1 in its least significant bit. Let prisoner 10 take a sip from every bottle with a 1 in its most significant bit. etc.

prisoner = 10 9 8 7 6 5 4 3 2 1

bottle 924 = 1 1 1 0 0 1 1 1 0 0

For instance, bottle no. 924 would be sipped by 10,9,8,5,4 and 3. That way if bottle no. 924 was the poisoned one, only those prisoners would die.

After four weeks, line the prisoners up in their bit order and read each living prisoner as a 0 bit and each dead prisoner as a 1 bit. The number that you get is the bottle of wine that was poisoned.

1000 is less than 1024 (2^10). If there were 1024 or more bottles of wine it would take more than 10 prisoners.

**Age Puzzles**

**Puzzle:**

Salman’s youth lasted one sixth of his life. He grew a beard after one twelfth more. After one seventh more of his life, he married. 5 years later, he and his wife had a son. The son lived exactly one half as long as his father, and salman died four years after his son.How many years did salman live?

**Answer:**

x/6 + x/12 + x/7 + 5 + x/2 + 4 = x

where x is salman’s age at the time of his death.

Therefore, salman lived exactly 84 years.

**Inverted Triangle Puzzle**

**Puzzle:**

Triangle is constructed from 10 coins. What is the smallest number of coins that need to be moved to make the triangle point downwards?

**Answer:**

**Birds and Flower Puzzle**

**Puzzle:**

Once there came many birds to a pond. There were certain number of lotus flowers in the pond. If each bird occupied one lotus one bird was left alone without any flower. If two birds sat in a flower one flower was left behind. Find the total number of birds and flowers.

**Answer:**

There are 4 lotus flowers and 3 birds. Let the 0s represent the birds. Let the 1s represent the lotus flowers.

*CASE 1:*

Each bird sat on each lotus flower, one bird was left alone. 1 1 1 1 0 0 0

*CASE 2:*

Two birds sat on each lotus flower, one flower was left alone. (1 1) (1 1) 0 0 0

**Time and Machines**

**Puzzle:**

If it takes 5 machines 5 minutes to make 5 widgets, how long would it take 100 machines to make 100 widgets?

**Answer:**

5 Minutes