In this post I am presenting 3 such interesting puzzles. Keen observation and simple application of logic is required to solve them. So here you go -

1. Make this equation valid with single stroke of pen (i.e. just by adding a line somewhere): 5+5+5 = 550
2. Make 120 using 5 zeros. You can use any mathematical notation/symbol
3. What mathematical symbol can be put between 5 and 9, to get a number bigger than 5 and smaller

Leave your answers as comment under this post.

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Your grandfather, determined to start the year 1900 off right, went to bed at 7 p.m. on December 31, 1899, setting his alarm clock to wake him at 8 the next morning. He slept like a log. How many hours sleep did he get?

Ancient Coin Puzzle

A thief went to a shop that sold antique coins. He stole a coin from Emperor Alexander’s time that had 326 B.C. inscribed on it. These rare coins were worth $ 100 for every year of their age (years from date of minting till now). So how much did the thief get for his stolen coin?

Both the puzzles above have some similarity. There is a clue hidden in the title of the post itself.

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Three friends check into a hotel. They pay $30 to the manager and go to their room. The manager suddenly remembers that the room rate is $25 and gives $5 to the bellboy to return to the people.  On the way to the room the bellboy reasons that $5 would be difficult to share among three people so he pockets $2 and gives $1 to each person. Now each person paid $10 and got back $1. So they paid £9 each, totalling $27. The bellboy has $2, totalling $29.

Where is the missing $1?

leave your answers below.

The above  missing dollar riddle is a famous problem that illustrates problems of confusion and misdirection in conversation. It illustrates how misdirection and irrelevant facts and questions can foil a person's clear understanding of a problem. Apply your mind and explain the logic behind the missing dollar.

Follow-up to the above problem - An interesting resolution is often cited as the solution to the above problem. Just read the following paragraph and post a comment whether you agree or not the given resolution to the above mystery.

A few months later, two of the original three guests check into a hotel room in the same hotel. The clerk says the bill is $20, so each guest pays $10. Later the clerk realizes the bill should only be $15. To rectify this, he gives the bellhop $5 to return to the guests. On the way to the room, the bellhop realizes that he cannot divide the money equally. As the guests didn't know the total of the revised bill, the bellhop decides to just give each guest $1 and keep $3 for himself.

Now that each of the guests has been given $1 back, each has paid $9, bringing the total paid to $18. The bellhop has $3, so $18 + $3 = $21, and the guests originally handed over $20, so that's where the missing dollar from the original problem is!

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Timing Puzzle 1
Having 2 sand-glasses: one 7-minute and the second one 4-minute. How can you time correctly 9 minutes ?

Timing Puzzle 2
A teacher of mathematics used an unconventional method to measure a 15-minute time limit for a test. He just used 7 and 11-minutehourglasses. During the whole time he turned sandglasses only 3 times (turning both hourglasses at once count as one flip).

Explain how the teacher measured 15 minutes.

Leave your answers below

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During the latest round of a game, Kamal was fourth. Ramesh is not the oldest, but is older than Sujan, who was not second. The child who was next in age to the youngest, finished second. The child who finished in third place is older than the child who finished first. Bimal is younger than the child who finished in third place. Can you determine who finished where and place the children in order of age?

Leave your answers below -

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12 coins 3 weighings

You have 12 coins, one of which is fake. The fake coin is indistinguishable from the rest except that it is either heavier or lighter, but you don't know which. Can you determine which is the fake coin and whether it is lighter or heavier using a balance scale and only 3 weighing?

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Grid Puzzle

Below is a very special grid, around each shaded number are 8 white squares. However, each white square should have a number from 1 to 7. Once filled in, these 8 numbers will sum to the shaded number. In addition, once completed correctly, no row nor column will contain a duplicate number within a white square. For example, the top row may be 5 6 4 2 3 1 7, etc. hence no digit repeated (similar to Sudoko)

Try to fill all the blank spaces. Leave your answers below by writing the numbers row-wise.

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Answer (posted on September 17, 2010)

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I met Sweety first time in a marriage party in Kolkata. We exchanged our phone numbers and decided to meet each other soon. When she rang up and invited me to her house, she decided to tease me.

This is how she gave me the number of her house on a particular street:

“I live in a long street. Numbered one the one side of my house are the houses one, two, three and so on.  All the numbers on one side of my house add up to exactly the same as all the numbers on the other side of my house. I know there are more than 50 houses on that side of the street, but not so many as 500”

Can you help me find Sweety’s House number?

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If you divide the number of eggs by 2 there will be one egg left.
If you divide the number of eggs by 3 there will be one egg left.
If you divide the number of eggs by 4 there will be one egg left.
If you divide the number of eggs by 5 there will be one egg left.
If you divide the number of eggs by 6 there will be one egg left.
If you divide the number of eggs by 7 there will be one egg left.
If you divide the number of eggs by 8 there will be one egg left.
If you divide the number of eggs by 9 there will be one egg left.
If you divide the number of eggs by 10 there will be one egg left.
Finally. If you divide the Number of eggs by 11 there will be NO EGGS left!
How many eggs did the old lady have?

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