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logic1to10 (Logic problems)

Logic problems (‘brain teasers’) — Problems 1 to 10

The ten problems are presented first, followed by the solutions to the ten problems.

Problem 1:

Crossing the bridge: During a war, there was a bridge between two countries that was heavily guarded on the east side.  A sentry tower on the east side was manned 24 hours a day.  Every 3 minutes, a guard would come out of the tower to check on the bridge.  His orders were to turn back anyone who was trying to cross the bridge to come to the east and to shoot anyone who was trying to get out of the country by fleeing the east and escaping to the west.  A woman desperately wanted to get into the western country.  She knew that it would take her five minutes to cross the bridge, but she managed to do it.  How did she cross from east to west, using the bridge?

Problem 2:

What is special about the following sequence of numbers?   8, 5, 4, 9, 1, 7, 6, 10, 3, 2, 0

Problem 3:

A large truck is to cross a one mile-long bridge.  The bridge has an exact weight limit of 14,000 pounds.  A fully-loaded truck, including the driver, weighing exactly 14,000 pounds, begins to cross the bridge.  The truck is safely half-way across the bridge when the driver abruptly stops the truck.  At that moment, a small bird lands on the truck.  Does the bridge collapse?

Problem 4:

At precisely 7 o’clock, a train enters a tunnel on the only track that runs through that tunnel, heading west.  Another train enters the opposite end of that same tunnel at precisely 7 o’clock on the same day, heading east.  There is only one train track that passes through the tunnel, with no side tracks.  Both trains travel through the tunnel safely and without incident.  How?

Problem 5:

A completely black cat was walking down the street during a total blackout — electricity was down throughout the entire town.  Not a single streetlight was functioning in the city.  Just as the cat was crossing a street, a car with two broken headlights came racing toward the cat.  As the car got to the spot where the cat was crossing the road, it swerved out of the way and avoided hitting the cat.  Remembering that the cat was COMPLETELY black, how did the driver of the car swerve the car and miss the cat?

Problem 6:

A man wants to fill a barrel exactly half full with water, using a hose.  The barrel has no markings, and no measuring devices are available.  The clever man successfully fills the barrel halfway.  How?

Problem 7:

A boy approached a ‘guess your weight’ booth at a carnival.  The booth attendant said to the boy, “If I can write your exact weight on this piece of paper, then you have to pay me $1.  However, if I can’t do that, then I will pay you $5.”  The boy was confident that the attendant couldn’t guess his exact weight, so he took the challenge.  The attendant took the paper, wrote on it, and handed it to the boy.  The boy, incredulous, handed the attendant a $1 bill.  How did the attendant accomplish this incredible fete?

Problem 8:

An Arabian sheikh had two sons, but only one could inherit the throne.  The sheikh devised a contest to determine which of his sons would be his successor.  The sons would race their camels to a distant city, and the winner would be the son whose camel arrived LAST in the city.  The sons started the race, and each one wandered aimlessly for days, not wanting to reach the city first.  They happened upon a wise man and each son asked his advice.  After hearing the wise man, both sons jumped on the camels and raced as fast as possible to the city.  What advice did the wise man give the sons?

Problem 9:

Twelve flies have landed on the table in front of me.  I smash four of the flies with a flyswatter.  How many flies remain on the table?

Problem 10:

Using only eight 8’s and addition signs, can you create an addition problem with the sum equal to 1000?

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Solution to Problem 1:

  • The woman started crossing the bridge as soon as the sentry went back into his tower.  After 2 minutes and 50 seconds had elapsed, she turned around and started walking back to the east.  The sentry came out exactly at the 3 minute mark and saw a woman walking toward him, moving from west to east.  His instructions were to send back anyone trying to come from the west into the east.  He ordered the woman to turn around and go back to the west.  She did so with a huge smile on her face.

Solution to Problem 2:

  • The numbers are listed in alphabetical order!

Solution to Problem 3:

  • No.  The fuel used up in driving half a mile easily offsets the weight of the bird.

Solution to Problem 4:

  • Simple — one train entered the tunnel at 7 am and the other at 7 pm.

Solution to Problem 5:

  • The entire scenario took place during the day.  It didn’t matter that the electricity was out — everyone could see just fine in broad daylight.

Solution to Problem 6:

  • As the water was running into the barrel, the man tipped the barrel sideways.  When the water reached the lip of the barrel and, at the same time, just covered the bottom of the barrel, the man knew that the barrel was exactly half full!

Solution to Problem 7:

  • Written on the paper were the following words: “Your exact weight.”

Solution to Problem 8:

  •    The wise man told each of the young men to immediately jump on his brother’s camel and gallop to the city!

Solution to Problem 9:

  • The four smashed flies remain on the table, and the other 8 fly away.  There must be 4 flies remaining on the table.

Solution to Problem 10:

  • 888 + 88 + 8 + 8 + 8 = 1000

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