1,128 Hard Riddles With Answers - page 11 of 12
Three doctors say James is their brother; James says he has no brothers.
This is a lateral thinking puzzle where the solution relies on a non-obvious interpretation of the words used.
Single thumb, four fingers, not alive.
Think about the literal properties of a 'a glove.'. The riddle uses metaphors to describe its physical form or function.
Around for years, but never older than a month.
Think about the literal properties of a 'the moon.'. The riddle uses metaphors to describe its physical form or function.
Something you can hold without using your arms.
Think about the literal properties of a 'your breath.'. The riddle uses metaphors to describe its physical form or function.
Begins and ends with T and has T inside it.
Think about the literal properties of a 'a teapot.'. The riddle uses metaphors to describe its physical form or function.
Has to be broken before you can use it.
Think about the literal properties of a 'an egg.'. The riddle uses metaphors to describe its physical form or function.
Sits when it stands, jumps when it walks.
Think about the literal properties of a 'a kangaroo.'. The riddle uses metaphors to describe its physical form or function.
I live in light, but if light shines on me, I die.
A shadow only exists when light is present but blocked. If you shine a light directly 'on' it (remove the blockage), it disappears.
Stone inside a tree, helps words live; stand still and have less the more I move.
A pencil contains graphite ('lead' from a mine) encased in wood (from a tree). It gets shorter as you use it.
Two fathers and two sons catch one fish each, but only bring home three.
This is a lateral thinking puzzle where the solution relies on a non-obvious interpretation of the words used.
Measure 1 cup using a 3-cup and 5-cup container.
This is a lateral thinking puzzle where the solution relies on a non-obvious interpretation of the words used.
Loses its head every morning, gets it back at night?
Think about the literal properties of a 'a pillow.'. The riddle uses metaphors to describe its physical form or function.
Monkey and squirrel climb a coconut tree; who gets the banana first?
Think about the literal properties of a 'neither '. The riddle uses metaphors to describe its physical form or function.
No legs, brown, has a head and tail?
Think about the literal properties of a 'a penny.'. The riddle uses metaphors to describe its physical form or function.
Paul is 9ft tall, wears size 12 shoes, and works at a butcher shop. What does he weigh?
Think about the literal properties of a 'meat.'. The riddle uses metaphors to describe its physical form or function.
Logic puzzle: 14 boys, 8 blue shirts, 2 neither, 5 boys in blue. Total class?
Think about the literal properties of a 'nineteen.'. The riddle uses metaphors to describe its physical form or function.
Parents have 6 sons, each has one sister. How many in the family?
Think about the literal properties of a 'nine .'. The riddle uses metaphors to describe its physical form or function.
Word with five letters that becomes smaller if you add two letters?
Think about the literal properties of a 'short '. The riddle uses metaphors to describe its physical form or function.
Sundial has the least moving parts; what has the most?
Think about the literal properties of a 'an hourglass '. The riddle uses metaphors to describe its physical form or function.
Odd one out: Snap, letter, mood, or stun?
This refers to the literal placement of the character in the spelling of the words 'April' and 'March'.
Cat crosses a river without getting wet or using a device.
This is a lateral thinking puzzle where the solution relies on a non-obvious interpretation of the words used.
Photo riddle: "I have no siblings, but this man's parent is my parent's son."
Think about the literal properties of a 'his son.'. The riddle uses metaphors to describe its physical form or function.
Most romantic part of the ocean?
This is a lateral thinking puzzle where the solution relies on a non-obvious interpretation of the words used.
Use me to stop, take me to smoke, pool's first stroke.
Think about the literal properties of a 'brake/break.'. The riddle uses metaphors to describe its physical form or function.
Some say I am green, red, or yellow. Some play with us; others spray us.
Think about the literal properties of a 'pepper.'. The riddle uses metaphors to describe its physical form or function.
Statements: "I have at least one daughter," "I have less than ten," "I have more than ten." Only one is true.
Think about the literal properties of a 'nan'. The riddle uses metaphors to describe its physical form or function.
Hiked south 3 miles, east 3, north 3. Back at camp, I see a bear. What color is it?
Think about the literal properties of a 'white'. The riddle uses metaphors to describe its physical form or function.
The first is higher, the second is wet; the whole ties or causes a cramp.
Think about the literal properties of a 'a hyphen.'. The riddle uses metaphors to describe its physical form or function.
The eyes will harvest, but the hand will sow.
This is a lateral thinking puzzle where the solution relies on a non-obvious interpretation of the words used.
I run, and it runs. When I stop, it still runs.
Think about the literal properties of a 'a watch.'. The riddle uses metaphors to describe its physical form or function.
How can you stand physically behind your mother while she stands behind you?
This is a lateral thinking puzzle where the solution relies on a non-obvious interpretation of the words used.
What is in a minute once and twice in a moment, but not in a thousand years?
This refers to the literal placement of the character in the spelling of the words 'April' and 'March'.
You eat me first, but then you get eaten.
The 'broken glass' was a fish tank. Without water, the fish died on the floor.
How is the number seven different from other numbers between one and ten?
This is a lateral thinking puzzle where the solution relies on a non-obvious interpretation of the words used.
Think of snow and clouds. What does a cow drink?
Think about the literal properties of a 'water.'. The riddle uses metaphors to describe its physical form or function.
What is something that belongs to you that everyone else uses?
Your name is your personal property, but people use it to address you more often than you use it to address yourself.
I am surrounded by wood, but I came from a mine. Everyone uses me.
A pencil contains graphite ('lead' from a mine) encased in wood (from a tree). It gets shorter as you use it.
I am in the middle of April and March, but not at the beginning or end of either.
This refers to the literal placement of the character in the spelling of the words 'April' and 'March'.
I have water but no fish, mountains but no trees, towns but no homes.
A map is a symbolic representation; it shows the locations of mountains and water without being made of rock or containing actual fish.
A prisoner is told: "If you tell the truth, I will shoot you; if you tell a lie, I will stab you." What should he say?
This creates a paradox. If the guard stabs him, his statement was true, but the guard should have shot him for telling the truth.
What can you feed to make it live, but give it a drink and it will die?
Fire needs fuel (food) to stay alive but is extinguished by water (a drink).
What type of room has no windows or doors?
A mushroom is a fungus, but the word contains 'room'. It doesn't have the structural features of a building like windows.
If you dropped me from a tall building, I would be fine. If you put me in the water, I would die.
Paper is light enough to survive a fall without breaking, but water will dissolve its fibers and 'kill' its form.
In the first stages of my life, I am taller than I will be in my last stages.
A candle is tall when first lit (young) and becomes shorter as it burns down (gets older).
Who buys this but has no use for it, makes it but doesn�t need it, and uses it but can�t feel it or see it?
The carpenter makes it for profit, the buyer buys it for someone else, and the person inside is dead and cannot see or feel it.
What has a corkscrew on one side and a power socket on the other?
This describes a pig's anatomy: a curly 'corkscrew' tail and a snout that resembles a two-pronged 'power socket'.
There are two of us, and we are sisters. We are on different sides of a road, but we are unable to view each other.
Your eyes are separated by your nose (the 'road'). Since they both face forward, they cannot see each other.
What has both wheels and flies but is not an aircraft?
This is a play on the word 'flies'. A garbage truck has wheels and attracts literal flies (insects) due to the trash it carries.
What is one time that a man can have an empty coat pocket, but have something in it at the same time?
A hole is technically 'something' that exists in the fabric, but it means the pocket contains no items, making it empty.
Payoff 2n (St. Petersburg). Charge to play?
The mathematical expectation is infinite, but most people wouldn't pay more than �20. This illustrates that humans value money based on 'utility' rather than just the raw expected amount.
Probability to be the last to try pitcher?
This is a property of a 'random walk' on a circle. Every person is equally likely to be the last one reached before the circle is completed.
Surprise test impossible logic?
If the test hasn't happened by Thursday, the students know it must be Friday (so it's not a surprise). This logic continues backward to Monday, 'proving' it can never be a surprise.
Sphere or Torus using rocks?
On a sphere, any two 'great circles' must intersect. On a torus, you can have a loop that goes around the center and another through the hole that never meet.
Hourglass weigh more falling or at rest?
When sand is in the air, its weight isn't recorded by the scale. However, the force of the sand hitting the bottom is greater than its static weight, resulting in a net increase during the flow.
1 poisoned bottle in 1000. Prisoners needed?
Give each prisoner a unique combination of bottles to sip from based on binary (0 and 1). The specific combination of prisoners who get sick creates a binary code for the poisoned bottle number.
P1 (4 of kind), P2 (3 of kind). Worst possible hand?
If Player 1 has four of a kind and Player 2 has three of a kind, there must be at least three cards of the same rank on the shared board. Your hand will use those same three cards.
Break stick at 2 random points. Triangle prob?
Using the 'triangle inequality' theorem, no piece can be longer than 0.5m. Visualizing this on a 2D plot of possible break points shows the 'success' area is 1/4 of the total area.
Camel 3000 bananas, 1k km. Max reach?
The camel must leave 'caches' of bananas. To minimize the 'cost' of travel, he moves the bananas in stages until the total supply matches his max capacity for the remaining distance.
Spheres with 6cm holes. Which has more volume?
The volume of a spherical ring depends only on the height of the hole (h). The formula V = (pi * h^3) / 6 shows the radius (R) of the original sphere cancels out.
Irrational number ^ irrational power = rational?
Consider x = sqrt(2)^sqrt(2). If x is rational, we are done. If x is irrational, then x^sqrt(2) = (sqrt(2)^sqrt(2))^sqrt(2) = sqrt(2)^2 = 2, which is rational.
1st sits random. Last gets assigned seat prob?
This is a classic probability puzzle. Either the first person takes your seat, or they take their own, or they take someone else's which triggers a chain that eventually hits yours or theirs.
100 cheating husbands. Execution day?
If there was 1 cheater, his wife would know immediately. If 2, they wait to see if the other wife acts. By the 100th day, the lack of action by others proves your own husband is one.
Truth 3/4 times. Says 6 on a die. Prob it's a 6?
The probability he says 6 AND it is 6 is (1/6 * 3/4). The probability he says 6 but it isn't 6 is (5/6 * 1/4). Use Bayes to find the ratio.
5 bandits split 100 coins. Senior proposal?
The senior bandit knows he only needs two other people to agree. He offers 1 coin to those who would get nothing in the next-best scenario to secure their vote.
Families stop childbearing after 1st boy. Sex ratio?
Every individual birth has a 50/50 chance. No matter the 'stopping rule,' the total expected number of boys and girls in the population will remain equal.
4 people: 1, 2, 5, 10 mins. Bridge (max 2). Min time?
Fastest pair (1&2) cross (2m), 1 returns (1m), slowest pair (5&10) cross (10m), 2 returns (2m), fastest pair (1&2) cross again (2m). 2+1+10+2+2 = 17m? Wait, logic says 15m is possible.
3 doors: Heaven, 1-day Hell, 2-day Hell. Avg days?
E = 1/3(0) + 1/3(1+E) + 1/3(2+E). Solving for E: E = 1 + 2/3E -> 1/3E = 1 -> E = 3.
110m rope. 1ft slack added/pulled up. Truck fits?
Adding 1ft of slack to 110m (360ft) creates a triangle with base 180 and hypotenuse 180.5. sqrt(180.5^2 - 180^2) = 13.4 ft, plenty for a truck.
Which is greater: e? or ?e?
Take the e-th root of both. e^(1/e) is the maximum value for the function x^(1/x). Since e is the base of the maximum, e^pi > pi^e.
Surgeon with 2 gloves must operate on 3 patients. How?
Patient 1: Gloves A and B. Patient 2: Only Glove B (top one removed). Patient 3: Turn Glove A inside out and put it over B. A's clean side is now outside.
Duck in pond. Cat runs 4x faster on edge. Escape?
The duck swims in a circle of radius R/4. The cat has to run halfway around the pond (pi * R). The duck's distance is shorter than the cat's travel time allows for.
1/4 into tunnel. Meet train at start or end. Speed ratio?
If she meets the train at the end after running 3/4 of the way, and she would have met it at the start after running 1/4 back... set up the time/distance equations.
Sum of digits from 1 to 1,000,000?
The sum for 0-999,999 is (sum of digits 0-9) * (number of positions) * (frequency). 45 * 6 * 100,000 = 27,000,000. Add 1 for the '1' in 1,000,000.
Helium balloon in car accelerating forward. Direction?
In an accelerating car, heavier air is pushed to the back. This creates a pressure gradient that 'buoys' the lighter helium balloon toward the front.
100 ants on 1m stick at 1cm/s. Max time to clear?
Because all ants are identical, a 'bounce' is mathematically the same as two ants passing through each other. The max time is just the time for the furthest ant to walk to the end.
Shortest distance from room corner to opposite corner?
Imagine the room as a flat 2D net. The shortest path is a straight line across two adjacent 'unfolded' faces of the room.
3-way. Accuracy 33/50/100. You (33) go first. Action?
If you miss on purpose, the 50% shooter will try to kill the 100% shooter (his biggest threat). This leaves you a 1-on-1 duel against a surviving, possibly weaker, opponent.
Alex (RR/BB wins). Sam (BR/RB wins). Better position?
Variance measures risk. Sam's payouts are always �2 for mixed colors, while Alex fluctuates between �3 and �1. Lower variance is 'safer' for the same return.
7-part bar. Pay 1 part/day for 7 days. Snap twice?
Binary counting: Pieces of 1, 2, and 4 units can be combined to form any total from 1 to 7. You swap pieces with the gardener daily like giving change.
3R, 2B hats. 1st/2nd can't guess. What is 3rd's color?
If the 3rd professor saw two blue hats, he would know his is red (only 2 blue exist). Since he doesn't know, the others must have at least one red hat... follow the deduction chain.
6 chambers, 2 consecutive bullets. Fired empty. Spin or stay?
Two bullets in 6 chambers leaves 4 empty slots. Since you just fired an empty one, there are 5 slots left; only one of the empty slots is followed by a bullet. 1/4 chance vs 1/3 if you spin.
Times digit "3" is printed between 3,000 and 4,000?
The digit 3 appears 1,000 times in the thousands place (3000-3999) and 100 times in each of the other three places (hundreds, tens, units) within that range.
54 cards (2 Jokers). Probability both are Jokers?
First Joker: 2/54. Second Joker: 1/53. Multiply them: 2 / (54 * 53) = 2 / 2862 = 1 / 1431.
1/1000 trick coin. Flip 10 heads. Prob it's the trick coin?
Bayes' Theorem: Prior prob of trick coin is 0.001. Prob of 10 heads given trick is 1. Given fair is (1/2)^10 = 1/1024. These are almost equal, so probability is about 0.5.
100B and 100W pearls. Maximize chance of picking Black.
Putting 1 black pearl in Sack A gives a 100% chance if A is picked. Sack B then has 99B/100W (~50%). Total chance: 0.5(1) + 0.5(0.497) = 74.85%.
Two 1-hr ropes, burn inconsistently. Measure 45 mins?
Lighting both ends of a 60m rope makes it burn in 30m. By lighting one end of Rope 2 at the same time, it has 30m left when Rope 1 finishes. Lighting its other end then gives 15m.
Black win $1, Red lose $1. Quit anytime. Strategy?
The expected value changes with every card drawn. If you have drawn more red than black, your chances of winning improve, and vice versa.
25 horses, 5-horse races. Min races to find top 3?
Race 5 groups of 5. Race the 5 winners (Race 6). Only the winner of Race 6, 2nd/3rd of that race, and specific others from their groups can be top 3. Race 7 decides.
Flip 4 coins. At least 2 are tails. Probability exactly 3 are tails?
Total outcomes are 16. Out of 16, 11 have >= 2 tails. Out of those 11, exactly 4 outcomes have 3 tails {TTTH, TTHT, THTT, HTTT}.
Joey/Charlie share 50ml. Joey sips 1/2, Charlie 1/2 of rest, repeat...
This forms a geometric series: Joey = 1/2 + 1/8 + 1/32... Charlie = 1/4 + 1/16 + 1/64... Summing them gives Joey 2/3 and Charlie 1/3 of the total.
Measure 9 mins using 4-min and 7-min hourglasses.
Run both. When 4 ends, 3 mins are left in 7. Flip 4. When 7 ends (7m total), 1 min is left in 4. Flip 7. When 4 ends (8m total), 1 min has run into 7. Flip 7 back to get that 1m.
How many times in 24 hours do clock hands form a 90� angle?
There are 22 such instances in 12 hours (2 per hour, but reduced by overlapping positions at 3 and 9). Thus, 44 times in 24 hours.
Family has 2 kids, one is a boy. Probability the other is a girl?
The possibilities for two children are {BB, BG, GB, GG}. Knowing one is a boy eliminates GG. The remaining set is {BB, BG, GB}. Two of these have a girl: {BG, GB}.
100 people flip switches of multiples of their entry. How many stay on?
A bulb ends up 'on' if its switch is flipped an odd number of times. Only numbers with an odd number of divisors (perfect squares) satisfy this.
2 A and 2 B pills identical. Hand has 1A, 2B. How to get correct dose?
By adding another A pill, you have 2 A's and 2 B's. Cutting each in half and taking one half of each ensures you get exactly 1 A and 1 B total.
10x10x10 cube painted then cut into 1x1x1s. How many have no paint?
Removing the outer layer of cubes leaves an inner cube of dimensions (10-2)x(10-2)x(10-2), which is 8x8x8 = 512.
3-pointer (40% win) or 2-pointer (70% tie, then 50% OT win)?
Winning with a 3-pointer is 40%. For the 2-pointer, the win probability is 70% (to tie) * 50% (to win OT) = 35%. 40% > 35%.
Two men in a desert. One is dead (pack closed), one is alive (pack open).
The man died because his parachute (the 'pack') failed to open.
What is 73? chicken, 32? cat and 42? goat?
Taking parts of the words: CHI-cken, CA-t, and GO-at spells Chicago.
What English word has three consecutive double letters?
"Bookkeeper" contains oo, kk, and ee back to back, three double letters in a row.