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22 Logic Puzzles To Exercise Your Mind

logic puzzles

Looking for a little mental challenge? Test your cerebral fortitude with 22 tricky logic puzzles and riddles.

1. Water Jugs

Q: You have a 5-gallon jug , a 3-gallon jug and a water faucet. How can you accurately pour 4 gallons of water into the 5-gallon jug?

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A: First fill the 5-gallon jug, then pour the 5-gallon jug into 3-gallon one until completely filled. 2 gallons are left in the 5-gallon jug. Empty the 3-gallon jug and pour the 2-gallons of water into it. Now refill the empty 5-gallon jug completely and then pour that into the 3-gallon until full. What remains in the 5-gallon jug should be 4 gallons.

2. The Hourglasses

Q: On a table sits two hourglasses. One contains 11 minutes of sand and the other contains 7 minutes of sand. Using just these 2 hourglasses, how can you accurately time 15 minutes?

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A: Flip both hourglasses. Once the 7 minute hourglass runs out, stop the 11 minute hourglass by turning it on it’s side. There are now 4 minutes remaining in the 11 minute glass. Now flip both glasses again and resume until the 11 minute hourglass runs out. At that point, stop the 7 minute hourglass by turning it on it’s side. There is now 4 minutes in the 7 minute hourglass. Now you can restart the 11 minute hourglass in it’s entirety and then follow it with the remaining 4 minutes left in the 7 minute hourglass, adding up to a total of 15 minutes.

3. The River Crossing

Q: A detachment of soldiers must cross a river. The bridge is broken and the river is deep. Thinking of what to do, suddenly the officer in charge spots two boys playing in a rowboat by the shore. The boat is so tiny, however, that it can only hold two boys or one soldier. Still, all the soldiers succeed in crossing the river in the boat.
How?

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A: First the boys cross the river. One stays ashore while the other brings the boat to the soldiers and gets out. A soldier gets in the boat and crosses. The boy who has stayed there brings the boat back to the soldiers, then takes the other boy back to the other shore. Again a boy brings the boat back out, a second soldier crosses over… until all the soldiers have crossed.

4. The Wolf, Goat and Cabbage

Q: A man has to take a wolf, goat and some cabbage across a river. His rowboat has enough room for the man plus either the wolf or the goat or the cabbage. If he takes the cabbage with him, the wolf will eat the goat. If he takes the wolf, the goat will eat the cabbage. Only when the man is present are the goat and the cabbage safe from their enemies. All the same, the man carries wolf, goat, and cabbage across the river. How?

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A: The man first takes the goat across since the wolf does not eat cabbage. The man returns and takes the cabbage across. He leaves the cabbage and takes the goat with him on his return trip exchanging it for the wolf that he then takes across. Leaving the wolf with the cabbage he returns for the goat which he brings across lastly.

5. How Old Am I?

Q: When my father was 31, I was 8. Now he is twice as old as I am. How old am I?

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A: 23 years old.

6. How Many Siblings?

Q: A boy has twice as many sisters as brothers, but each sister has only half as many sisters as brothers. How many brothers and sisters are in the family?

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A: 4.

7. A Logical Draw

Q: Three puzzle participants are blindfolded. A white card is glued to each one’s forehead and they are told that not all the cards are black. The blindfolds are removed and the prize goes to the one who can correctly deduce the color of his card. All three announce white at the same time. Why?

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A: Initially no one answered, because they could each see that the other two had a white card but could be certain what color their own was. After a pause, they each realized they were experiencing the same dilemma which confirmed they in fact all had white cards.

8. Three Philosophers

Q: Three philosophers took a nap under a tree. While they were asleep, a prankster smeared their faces with charcoal. Upon waking they began to laugh, each thinking the other two were laughing at the other. Suddenly one man stopped laughing. How did he realize his own face was also smeared?

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A: A reasoned: “B is confident his own face is not smeared. If he saw mine unsmeared he would be surprised at C’s laughing, because C would have no smeared face to laugh at. But B is not surprised. Therefore, my face is smeared.

9. Making Change

Q: What is the maximum value of change that you can have in U.S. coins (pennies, nickels, dimes, and quarters) without being able to give someone exact change for a one-dollar bill?

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A: $1.19. One way using 3 quarters, 4 dimes, and 4 pennies. The second way using 1 quarter, 9 dimes, and 4 pennies.

10. Rope Burning

Q: You have two ropes. Each rope takes one hour to burn completely. Both ropes have varying thicknesses, meaning that different parts of each rope burn at different speeds. How can you accurately time forty-five minutes with just two ropes and a lighter?

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A: Light the first rope from both ends and the second rope from just one end. Once the first rope is completely burnt, you will know that thirty minutes have gone by and you will know that the second rope has thirty minutes left before it burns completely. As soon as the first rope is burnt, you light the other end of the second rope, which will double the rate of consumption and cut the remaining time of the rope in half, meaning that it will only take fifteen more minutes for the second rope to burn out completely. The thirty minutes from the first rope and the fifteen minutes from the second give you forty-five minutes.

11. Bridge Crossing

Q: Abe, Bill, Chris and Donald are all on one side of a narrow and dangerous bridge that they need to cross. It is late at night and very dark so they require a flashlight to cross safely. They have only one flashlight and the bridge is only strong enough to support the weight of two people at once. Each of the four people walk at different speeds: Abe can cross the bridge in one minute, Bill can cross in two minutes, Chris can cross in five minutes, and Donald can cross in ten minutes. When two people are walking together sharing the flashlight they can walk at the slower person’s pace.

How quickly can Abe, Bill, Chris and Donald cross the bridge safely?

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A: They can all cross in no less than 17 minutes. First Abe and Bob cross in two minutes. Abe returns in 1 minute with the flashlight. Chris and Donald cross the bridge in 10 minutes. Bob returns the flashlight in 2 minutes and then he and Abe cross again in 2 minutes.

12. Shashank Plan

Q: A man is imprisoned in a 10 ft. by 10 ft. by 10 ft. room. The walls are made of concrete, the floor is made of dirt. The only openings are a locked door and a skylight. The only tool he has is a small shovel with which he begins to dig a hole in the floor. The man knows it is impossible to tunnel out of his prison cell but continues anyway.

What is the man’s plan?

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A: All the man is trying to do is dig enough dirt so he can make a pile large enough to reach the skylight.

13. Between Two Trees

Q: You are standing at the edge of a lake. The lake is 500 feet in diameter and there is a small island in the middle of it. Next to you is a large tree and in the middle of the island there is a tree also. You cannot swim but you have a rope that is a little over 500 feet long. How can you use the rope to reach the island?

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A: First tie one end of the rope to the tree next to you. Then, while holding the other end, walk all the way around the lake perimeter. The rope will wrap around the tree at the center of the island. You can now secure the rope to the tree next to you creating a bridge to the island.

14. Five Apples

Q: Five apples are in a basket. How do you divide them among five girls so that each girl gets an apple but one apple remains in the basket?

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A: Give the fifth girl her apple with the basket.

15. Cats

Q: How many cats are sitting in a small room if in each of the four corners a cat is sitting, and opposite each cat there sit three cats, and at each cat’s tail sits another cat.

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A: Four cats, each near the tail of a cat in an adjacent corner.

16. Broken Chain

Q: A metal smith needs to join five short pieces of chain into one long chain. Each segment contains three links each. He could easily complete this task in 8 steps of opening and closing links, but the metal smith believes he can do it in 6 steps.
How?

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A: He opens all 3 rings of 1 piece (3 operations). With these he links the other 4 pieces together.

17. Eating Garbage

Q: Your friend tells you his favorite food is the one where you throw away the outside and cook the inside, then you eat the outside and throw away the inside. What food is he talking about?

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A: Corn on the cob. You throw away the husk then cook the corn that is inside, then eat the corn and throw away the core that is inside.

18. The Dove

Q: A wise old man lived in little house on a hill. One day, two young boys from town decided they wanted to fool the man. They took a dove with them and knocked on his door. When he opened, one of the boys said to him, “Let’s see how smart you really are! Is the dove I’m holding behind my back dead or alive?” The old man smiled and replied “I cannot answer you because I know you are trying to trick me.” Despite knowing the condition of the dove, why didn’t the old man answer the young boy?

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A: Because if he told them it was live, the boy would kill it behind his back. If he said it was dead, they would simply reveal the live dove.

19. Bear Hunting

Q: A famous hunter woke up early one morning and headed south to hunt bears after eating breakfast. After travelling a mile south he spotted a bear, aimed his gun fired and missed. The bear was frightened and headed east. The hunter followed the bear and caught up with it after travelling half a mile. He shot the bear this time but only wounded it. The bear limped another mile but the hunter finally shot and killed it. The hunter walked the mile back north to his cabin and discovered it being marauded by another bear.

What color was the bear that was tearing up the hunter’s cabin?

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A: The bear must have been a white polar bear. The only way for the hunter to have traveled the way he traveled and wind up back at his cabin would be if he were at the North Pole.

20. What Am I? #1

Q: I will munch on what you feed me
Although I am not greedy
I easily add many pounds
Without my weight increasing

I do not begrudge thee
when you push and punch me
I have no will or goal than to
Resolve that which you ask me

What am I?

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A: A calculator. It “crunches” numbers. It easily adds pounds (or any other unit of measure) via arithmetic. You “punch” in numbers by pushing it’s buttons. It gives you solutions.

21. What Am I? #2

Q: Sometimes I follow
At times I lead
Sometimes I move
Right under your feet
Although I’m not bright
I am light indeed
At night I leave
Your company
What Am I?

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A: A Shadow

22. What Am I? #3

Q: In water I’m born
On land I die
I’m like a cyclops
though I am blind
Although I have
no path in mind
Where I go
Death trails behind
What Am I?

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A: A Hurricane.

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Jetta Moon

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