Interesting Brain Teasers

I am taken from a mine, and shut up in a wooden case, from which I am never released, and yet I am used by almost everybody. Pencil lead
What goes round the house and in the house but never touches the house? The sun
What is it that you can keep after giving it to someone else? Your word
What walks all day on its head? A nail in a horseshoe
What gets wet when drying? A towel
What comes once in a minute, twice in a moment, but never in a thousand years? The letter M
What is round as a dishpan, deep as a tub, and still the oceans couldn't fill it up? A sieve
There were five men going to church and it started to rain. The four that ran got wet and the one that stood still stayed dry. Body in coffin, and bearers
The more you take, the more you leave behind. What are they? Footsteps
He who has it doesn't tell it. He who takes it doesn't know it. He who knows it doesn't want it. What is it? Counterfeit money
Brothers and sisters have I none but that man's father is my father's son. My son
Who spends the day at the window, goes to the table for meals and hides at night? A fly
I bind it and it walks. I loose it and it stops. A sandal
What goes round and round the wood but never goes into the wood? The bark of a tree
I went to the city, I stopped there, I never went there, and I came back again. A watch
I have a little house in which I live all alone. It has no doors or windows, and if I want to go out I must break through the wall. A chicken in an egg
Scarcely was the father in this world when the son could be found sitting on the roof. Fire, smoke
There are four brothers in this world that were all born together. The first runs and never wearies. The second eats and is never full. The third drinks and is always thirsty. The fourth sings a song that is never good. Water, fire, earth, wind
A cloud was my mother, the wind is my father, my son is the cool stream, and my daughter is the fruit of the land. A rainbow is my bed, the earth my final resting place, and I'm the torment of man. Rain
Poke your fingers in my eyes and I will open wide my jaws. Linen cloth, quills, or paper, my greedy lust devours them all. Shears (or scissors)
What is that which goes with a carriage, comes with a carriage, is of no use to a carriage, and yet the carriage cannot go without it? Noise
It stands on one leg with its heart in its head. A cabbage
It's been around for millions of years, but it's no more than a month old. What is it? The moon
A white dove flew down by the castle. Along came a king and picked it up handless, ate it up toothless, and carried it away wingless. Snow melted by the sun
As I went across the bridge, I met a man with a load of wood which was neither straight nor crooked. What kind of wood was it? Sawdust
What belongs to you but others use it more than you do? Your name
What goes up the chimney down, but can't go down the chimney up? An umbrella
What is is that you will break even when you name it? Silence
What fastens two people yet touches only one? A wedding ring
What is it the more you take away the larger it becomes? A hole
I am the beginning of sorrow, and the end of sickness. You cannot express happiness without me, yet I am in the midst of crosses. I am always in risk, yet never in danger. You may find me in the sun, but I am never out of darkness. The letter S
What is put on a table, cut, but never eaten? A pack of cards
Who are the two brothers who live on opposite sides of the road yet never see each other? Eyes
What holds water yet is full of holes? A sponge
Though it is not an ox, it has horns; though it is not an ass, it has a pack-saddle; and wherever it goes it leaves silver behind. What is it? A snail
Lives without a body, hears without ears, speaks without a mouth, to which the air alone gives birth. An echo
A hundred-year-old man and his head one night old. Snow on a tree stump
What goes into the water red and comes out black? A red-hot poker
What goes into the water black and comes out red? A lobster
When one does not know what it is, then it is something; but when one knows what it is, then it is nothing. A riddle
A
· Able was I ere I saw Elba.
· A dog! A panic in a pagoda!
· Age, irony, Noriega.
· Ah, Aristides opposed it, sir, aha!
· Ah, Satan sees Natasha.
· All erotic, I lose lame female solicitor Ella.
· Al lets Della call Ed, Stella.
· A man, a plan, a canal - Panama!
· "Amen!" I call if I fill a cinema.
· Amore? Roma!
· A new order began, a more Roman age bred Rowena.
· Anne, I stay a day at Sienna.
· Anne, I vote more cars race Rome-to-Vienna.
· A nut for a jar of tuna.
· A pain, a blast; ah, that's Albania, Pa!
· A pre-war dresser drawer, Pa.
· Are we not drawn onwards, we Jews, drawn onward to new era?
· Are we not, Rae, near to new era?
· A rod, not a bar, a baton, Dora.
· A Toyota: race fast, safe car: a Toyota.
· A Toyota's a Toyota.
B (Top)
· Ban campus motto: "Bottoms up, MacNab".
· Bob: "Did Anna peep?" Anna: "Did Bob?"
· Bog dirt up a sidetrack carted is a putrid gob.
· Borrow or rob.
· But Anita sat in a tub.
C (Top)
· Cain: a maniac.
· Cigar? Toss it in a can, it is so tragic!
· Civic sin, Alan, is civic.
· Cora sees a roc.
D (Top)
· Damn! I, Agassi, miss again! Mad!
· Damosel, a poem? A carol? Or a cameo pale? So mad!
· Deer breed.
· Deer flee freedom in Oregon? No, Geronimo - deer feel freed.
· Deer frisk, sir, freed.
· Degenerate Moslem, a cad! Eva saved a camel so Meta reneged.
· Deirdre wets altar of St. Simon's - no mists, for at last ewer dried.
· Delia and Edna ailed.
· Delia failed.
· Delia, here we nine were hailed.
· Delia sailed as sad Elias ailed.
· Delia sailed, Eva waved, Elias ailed.
· Delia's debonair dahlias, poor, drop or droop. Sail, Hadrian; Obed sailed.
· Deliver, Eva, him I have reviled.
· "Deliver desserts," demanded Nemesis, "emended, named, stressed, reviled."
· Dennis and Edna sinned.
· Dennis, Nell, Edna, Leon, Nedra, Anita, Rolf, Nora, Alice, Carol, Leo, Jane, Reed, Dena, Dale, Basil, Rae, Penny, Lana, Dave, Denny, Lena, Ida, Bernadette, Ben, Ray, Lila, Nina, Jo, Ira, Mara, Sara, Mario, Jan, Ina, Lily, Arne, Bette, Dan, Reba, Diane, Lynn, Ed, Eva, Dana, Lynne, Pearl, Isabel, Ada, Ned, Dee, Rena, Joel, Lora, Cecil, Aaron, Flora, Tina, Arden, Noel and Ellen sinned.
· Dennis, no misfit, can act if Simon sinned.
· Deny me not; atone, my Ned.
· Depardieu, go rap a rogue I draped.
· Desserts I desire not, so long no lost one rise distressed.
· Diana saw Dr. Awkward was an aid.
· Did Dean aid Diana? Ed did.
· Did Hannah say as Hannah did?
· Did Hannah see bees? Hannah did.
· Di, did I as I said I did?
· Did Ione take Kate? No, I did.
· Did I do, O God, did I as I said I'd do? Good, I did!
· Did I draw Della too tall, Edward? I did?
· Doc, note, I dissent, A fast never prevents a fatness. I diet on cod.
· Dog, as a devil deified, lived as a god.
· Do geese see God?
· Dogma: I am God.
· Do Good's deeds live on? No, Evil's deeds do, O God.
· "Do nine men interpret?" "Nine men," I nod.
· Do not start at rats to nod.
· Don't nod.
· Doom an evil deed, liven a mood.
· Doom, royal panic, I mimic in a play or mood.
· Dora tendered net, a rod.
· Drab as a fool, as aloof as a bard.
· Drab Reg, no longer bard.
· Drat Saddam! A mad dastard!
· Draw - aye, no melody - dole-money award.
· Draw no dray a yard onward.
· Draw, O Caesar, erase a coward.
· Draw, O coward!
· Draw pupil's pup's lip upward.
· Drowsy baby's word.
E (Top)
· E. Borgnine drags Dad's gardening robe.
· Ed: a general, a renegade.
· Ed, I saw Harpo Marx ram Oprah W. aside.
· Ed is on no side.
· Edith, cold-eyed, eyed loch tide.
· Egad, a base life defiles a bad age.
· Egad, a base tone denotes a bad age.
· Egad, an adage!
· Egad! Loretta has Adams as mad as a hatter. Old age!
· Egad! No bondage!
· Emil asleep, Allen yodelled "Oy!" Nella peels a lime.
· Emil asleep, Hannah peels a lime.
· Enid and Edna dine.
· Ere hypocrisies or poses are in, my hymn I erase. So prose I, sir, copy here.
· Euston saw I was not Sue.
· Euston sees not Sue.
· Eva, can I pose as Aesop in a cave?
· Eva, can I stab bats in a cave?
· Evade me, Dave.
· Eve damned Eden, mad Eve.
· Eve saw diamond, erred. No maid was Eve.
· Evil is a name of a foeman, as I live.
· Evil - a diamond, a cad - no maid alive!
· Evil odes or prose do live.
G (Top)
· Flee to me, remote elf.
· Flesh? Saw I Mimi wash self?
G (Top)
· Gate-man sees name, garage-man sees name-tag.
· Gert, I saw Ron avoid a radio-van - or was it Reg?
· Gnu dung.
· God, a red nugget! A fat egg under a dog!
· God, a slap! Paris, sir, appals a dog!
· Goddesses so pay a possessed dog.
· "Go, droop aloof," sides reversed, is "fool a poor dog".
· Go hang a salami! I'm a lasagna hog!
· Golf? No, sir, prefer prison-flog.
H (Top)
· Ha! I rush to my lion oily moths, Uriah!
· Ha! Jar level Rajah!
· Harass selfless Sarah.
· Harass sensuousness, Sarah.
· Ha! Robed Selim smiles, Deborah!
· Ha! Robed rats deliver reviled star, Deborah!
· He lived as a devil, eh?
· Hell! A spacecraft farce caps all, eh?
· Help Max, Enid, in example "H".
· Here so long? No loser, eh?
· He won a Toyota now, eh?
I (Top)
· If I had a hi-fi...
· I, madam, I made radio. So I dared! Am I mad? Am I?
· I made border bard's drowsy swords; drab, red-robed am I.
· I maim nine men in Saginaw; wan, I gas nine men in Miami.
· I maim nine more hero-men in Miami.
· I, man, am regal; a German am I.
· I, Marian, I too fall; a foot-in-air am I.
· I moan, "Live on, O evil Naomi!"
· In airy Sahara's level, Sarah, a Syrian, I.
· In a regal age ran I.
· I prefer pi.
· I, Rasputin, knit up sari.
· I roamed under it as a tired, nude Maori.
· I saw desserts. I'd no lemons, alas no melon. Distressed was I.
· I saw I was I.
· I saw thee, madame, eh? 'Twas I.
· "Is Don Adams mad?" A nod. "Si!"
· I tip away a wapiti.
· I told Edna how to get a mate: "Go two-handed." Loti.
J (Top)
· Jar a tonga, nag not a Raj.
K (Top)
· Kayak salad: Alaska yak.
· Kay, a red nude, peeped under a yak.
· Kay dated a cadet, a Dyak.
· "Knight, I ask nary rank," saith gink.
L (Top)
· La, not atonal!
· Lager, sir, is regal.
· Lapp, Mac? No, sir, prison-camp pal.
· Last fig - as a gift, Sal.
· Lay a wallaby baby ball away, Al.
· Lee had a heel.
· Lepers repel.
· Let O'Hara gain an inn in a Niagara hotel.
· Lew, Otto has a hot towel.
· Lid off a daffodil.
· Live dirt up a sidetrack carted is a putrid evil.
· Live not on evil.
· Live not on evil deed, live not on evil.
· Live not on evil, madam, live not on evil.
· Live, O Devil, revel ever, live, do evil.
· Live on, Time; emit no evil.
· Live was I ere I saw Evil.
· Loot: slate, metal plate, metal stool.
M (Top)
· Madame, not one man is selfless; I name not one, Madam.
· Madam, I'm Adam.
· Madam, in Eden I'm Adam.
· Ma handed Edna ham.
· Ma is a nun, as I am.
· Ma is as selfless as I am.
· "Ma," Jerome raps pot top, "spare more jam!"
· Man, Eve let an irate tar in at eleven a.m.
· Man, Oprah's sharp on A.M.
· Marge let a moody baby doom a telegram.
· Marge lets Norah see Sharon's telegram.
· Marge, let's "went". I await news telegram.
· Max, I stay away at six a.m.
· May a moody baby doom a yam?
· Milestones? Oh, 'twas I saw those, not Selim.
· Mirth, sir, a gay asset? No, don't essay a garish trim.
· Moorgate got nine men in to get a groom.
· Moors dine, nip - in Enid's room.
· Mother at song no star, eh Tom?
· Mother Eve's noose we soon sever, eh Tom?
· Mr. Owl ate my metal worm.
· Murder for a jar of red rum.
· Must sell at tallest sum.
N (Top)
· Name no-one man.
· Name now one man.
· Name tarts? No, medieval slave, I demonstrate Man!
· Naomi, did I moan?
· Ned, go gag Ogden.
· Ned, I am a maiden.
· Nella, demand a lad named Allen.
· Nella risks all: "I will ask Sir Allen."
· Nella's simple hymn: "I attain my help, Miss Allen."
· Nella won't set a test now, Allen.
· Nemo, we revere women.
· Never a foot too far, even.
· Never odd or even.
· Niagara, O roar again!
· No benison, no sin, Ebon.
· "No cab, eh, Ted?" I sat up. I put aside the bacon.
· No Dot nor Ottawa "legal age" law at Toronto, Don.
· Noel, did I not rub Burton? I did, Leon.
· Noel, let's egg Estelle on.
· Noel sees Leon.
· No evils Shahs live on.
· No garden, one dragon.
· No, Hal, I led Delilah on.
· No ham came, sir, now siege is won. Rise, MacMahon.
· No, I save on final perusal, a sure plan if no evasion.
· No, is Ivy's order a red rosy vision?
· No, it can assess an action.
· No, it is open on one position.
· No, it is opposed; Art sees Trade's opposition.
· No, it is opposition.
· No, it never propagates if I set a gap or prevention.
· No, it's a bar of gold, a bad log for a bastion.
· No lemons, no melon.
· No, Mel Gibson is a casino's big lemon.
· No miss, it is Simon.
· No Misses ordered roses, Simon.
· No mists or frost, Simon.
· Nomists reign at Tangier, St. Simon.
· Nora, alert, saws goldenrod-adorned logs. Wastrel Aaron!
· "Nora, a raft!" "Is it far, Aaron?"
· Norah's foes order red rose of Sharon.
· "Norah's moods," Naomi moans, "doom Sharon."
· Noriega can idle, held in a cage - iron!
· Nor I, fool, ah no! We won halo - of iron.
· Nor I nor Emma had level'd a hammer on iron.
· Norma is as selfless as I am, Ron.
· No, set a maple here; help a mate, son.
· "Not for Cecil?" asks Alice Crofton.
· Not I, no hotel; cycle to Honiton.
· "Not New York," Roy went on.
· Not nil, Clinton.
· Not seven on a mere man - one vest on.
· Not so, Boston.
· No waste, grab a bar, get saw on.
· "Now dine," said I as Enid won.
· Now do I repay a period won.
· Now ere we nine were held idle here, we nine were won.
· Now, Eve, we're here, we've won.
· Nowise I bury rubies I won.
· Now, Ned, I am a maiden nun; Ned, I am a maiden won.
· No word, no bond; row on.
· Now saw ye no mosses or foam, or aroma of roses. So money was won.
· Now, sir, a war is won.
· No "x" in "Mr. R. M. Nixon"?
· Nurse, save rare vases, run!
· Nurse, I spy gypsies, run!
· Nurse's onset abates, noses run.
O (Top)
· O desirable Melba, rise, do!
· O Geronimo, no minor ego!
· O gnats, tango!
· O had I nine more hero-men in Idaho!
· Oh, cameras are macho.
· O.J. nabs Bob's banjo.
· Oh who was it I saw, oh who?
· On tub, Edward imitated a cadet; a timid raw debut, no?
· O render gnostic illicit song, red Nero.
· O, stone, be not so.
· Otto made Ned a motto.
P (Top)
· Paget saw an Irish tooth, sir, in a waste gap.
· Paget saw a wasp in a waste gap.
· Part of U.S. is UFO trap.
· Party boobytrap.
· Pa's a sap.
· Pat and Edna tap.
· Peel's lager on red rum did murder no regal sleep.
· Plan no damn Madonna LP.
· Pooh, roll a ball or hoop.
· "Pooh," smiles Eva, "have Selim's hoop."
· Poor Dan is in a droop.
· Pull a bat! I held a ladle, hit a ball up.
· Pull up, Eva, we're here; wave, pull up.
· Pull up if I pull up.
· Pupils roll a ball or slip up.
· Pupils slip up.
· Pusillanimity obsesses Boy Tim in "All Is Up".
· Puss, a legacy! Rat in a snug, unsanitary cage, lass, up!
R (Top)
· "Rats gnash teeth," sang star.
· Rats live on no evil star.
· Raw was I ere I saw war.
· Red lost case, Ma. Jesse James acts older.
· Red Nevada vendor.
· Red now on level - no wonder.
· Redraw a warder.
· Red robber gazes not on S.E. Zagreb border.
· Red root put up to order.
· Red roses run no risk, sir, on nurse's order.
· Red rum, eh? 'Twas I saw the murder.
· Red rum, sir, is murder.
· Refasten gipsy's pig-net safer.
· Regard a mere mad rager.
· Reg, no lone car won, now race no longer.
· Re hypocrisy: as I say, sir, copy her.
· Remit Rome cargo to go to Grace Mortimer.
· Repel evil as a live leper.
· Resume so pacific a pose, muser.
· Retracting, I sign it, Carter.
· Revenge, Bill? I won! Will I beg? Never!
· Revenge my baby, Meg? Never!
· Revered now I live on. O did I do no evil, I wonder ever?
· "Reviled did I live," said I, "as evil I did deliver."
· "Revolt, love," raved Eva. "Revolt, lover!"
· Revolt on Yale, Democrats edit "Noon-Tide Star". Come, delay not, lover.
· Rise, morning is red, no wonder-sign in Rome, sir.
· Rise, take lame female Kate, sir.
· Rise to vote, sir.
· Ron, Eton mistress asserts I'm no tenor.
· Rot can rob a born actor.
· Roy Ames, I was a wise mayor.
· Roy, am I mayor?
S (Top)
· Sad? I'm Midas!
· Sail on, game vassal! Lacy callas save magnolias.
· Saladin enrobes a baroness, Señora, base-born Enid, alas!
· Salisbury Moor, sir, is roomy. Rub Silas.
· "Sal is not in?" Ruth asks. "Ah, turn it on, Silas."
· Satan, oscillate my metallic sonatas.
· Sat in a taxi, left Felix at Anita's.
· Satire: Veritas.
· Saw tide rose? So red it was!
· See few owe fees.
· See, slave, I demonstrate yet arts no medieval sees.
· Selim's tired; no wonder, it's miles.
· Semite, be sure! Damn a man-made ruse betimes!
· Senile felines.
· Set a broom on no moor, Bates.
· Sh! Tom sees moths.
· Sir, I demand, I am a maid named Iris.
· Sir, I'm Iris.
· Sir, I soon saw Bob was no Osiris.
· "Sirrah! Deliver deified desserts detartrated!" stressed deified, reviled Harris.
· Sis, ask Costner to not rent socks "As Is"!
· Sis, Sargasso moss a grass is.
· Sit on a potato pan, Otis.
· Si, we'll let Dad tell Lewis.
· Six at party; no pony-trap, taxis.
· "slang is not suet, is it?" Euston signals.
· Slap-dab set-up, Mistress Ann asserts, imputes bad pals.
· Snug satraps eye Sparta's guns.
· Snug was I ere I saw guns.
· So, Ida, adios!
· "So I darn on," a canon radios.
· Solo gigolos.
· So many dynamos.
· So may Apollo pay Amos.
· So may get Arts award. Draw a strategy, Amos.
· So may Obadiah aid a boy, Amos.
· So may Obadiah, even in Nineveh, aid a boy, Amos.
· Some men interpret nine memos.
· So remain a mere man. I am Eros.
· Sore was I ere I saw Eros.
· Spots tie - it's tops!
· Star? Come, Donna Melba, I'm an amiable man - no Democrats!
· Star comedy by Democrats.
· Stella won no wallets.
· Stephen, my hat! Ah, what a hymn, eh, pets?
· Step on hosepipes? Oh no, pets.
· Step on no pets!
· Stop! Murder us not, tonsured rumpots!
· "Stop!" nine myriad murmur. "Put up rum, rum, dairymen, in pots!"
· Stop, Syrian, I start at rats in airy spots.
· St. Simon sees no mists.
· Strategy: get arts.
· Straw? No, too stupid a fad. I put soot on warts.
· Sue, dice, do, to decide us.
· "Sue," Tom smiles, "Selim smote us!"
· "Suit no regrets." A motto, Master Gerontius.
· Sums are not set as a test on Erasmus.
· Swept pews? Yes, Sam Massey swept pews.
T (Top)
· Tarzan raised Desi Arnaz' rat.
· Telegram, Margelet!
· Ten animals I slam in a net.
· Ten dip a rapid net.
· Tenet C is a basis, a basic tenet.
· Tennis set won now Tess in net.
· Tennis tips: saliva. Vilas spits in net.
· Ten? No bass orchestra tarts, eh? Cross a bonnet.
· Tense, I snap Sharon roses or Norah's pansies net.
· Tessa's in Italy, Latin is asset.
· Tide-net safe soon, all in - a manilla noose fastened it.
· 'Tis Ivan on a visit.
· To last, Carter retracts a lot.
· To nets, ah no, son, haste not.
· Too bad, I hid a boot.
· Too far away, no mere clay or royal ceremony, a war afoot.
· Too far, Edna, we wander afoot.
· Too hot to hoot.
· Top step - Sara's pet spot.
· Top step's pup's pet spot.
· Tracy, no panic in a pony-cart.
· Trade ye no mere moneyed art.
· Trap all afoot; I too fall apart.
· Trap a rat! Stare, piper, at star apart!
· Trash? Even interpret Nineveh's art.
· Tulsa nightlife: filth, gin, a slut.
W (Top)
· War-distended nets I draw.
· Ward nurses run draw.
· Warsaw was raw.
· Was it a rat I saw?
· Was it Eliot's toilet I saw?
· Was it felt? I had a hit left, I saw.
· Was raw tap ale not a reviver at one lap at Warsaw?
· We freer few.
· We'll let Mom tell Lew.
· We name opera, rare poem, anew.
· We panic in a pew.
· We seven, Eve, sew.
· We, so to get a mate, go to sew.
· Wonders in Italy: Latin is "red" now.
· Won race, so loth to lose car now.
· Won't I repaper? Repaper it now.
· Won't lovers revolt now?
· Wonton on salad? Alas, no, not now!
X (Top)
· Xerxes was stunned! Eden nuts saw sex, Rex!
Y (Top)
· Yacht notes radar set on th' cay.
· Yawn a more Roman way.
· Yawn! Madonna Fan? No damn way!
· Ye slew Wesley.
· Yes, Mark, cable to hotel: "Back, Ramsey!"
· Yes, Syd, Owen saved Eva's new Odyssey.
· Yo! Bad anaconda had no Canada boy.
· Yo! Basil is a boy!
· Yo! Bottoms up! U.S. motto, boy!
· Yo! Breed deer, boy!
Z (Top)
· Zeus was deified, saw Suez.
The Damaged Engine
A Classic Puzzle by Henry Ernest Dudeney

We were going by train from Anglechester to Clinkerton, and an hour after starting an accident happened to the engine.We had to continue the journey at three-fifths of the former speed. It made us two hours late at Clinkerton, and the driver said that if only the accident had happened fifty miles farther on the train would have arrived forty minutes sooner. Can you tell from that statement just how far it is from Anglechester to Clinkerton?

The Damaged Engine
Solution

The distance from Anglechester to Clinkerton must be 200 miles.
The train went 50 miles at 50 m.p.h. and 150 miles at 30 m.p.h.
If the accident had occurred 50 miles farther on, it would have gone 100 miles at 50 m.p.h. and 100 miles at 30 m.p.h.
The Man and the Dog
A Classic Puzzle by Henry Ernest Dudeney

"Yes, when I take my dog for a walk," said a mathematical friend, "he frequently supplies me with some interesting puzzle to solve. One day, for example, he waited, as I left the door, to see which way I should go, and when I started he raced along to the end of the road, immediately returning to me; again racing to the end of the road and again returning. He did this four times in all, at a uniform speed, and then ran at my side the remaining distance, which according to my paces measured 27 yards. I afterwards measured the distance from my door to the end of the road and found it to be 625 feet. Now, if I walk 4 miles per hour, what is the speed of my dog when racing to and fro?"
The Man and the Dog
Solution

The dog's speed was 16 miles per hour.
The following facts will give the reader clues to the general solution. The distance remaining to be walked side by side with the dog was 81 feet, the fourth power of 3 (for the dog returned four times), and the distance to the end of the road was 625 feet, the fourth power of 5. Then the difference between the speeds (in miles per hour) of man and dog (that is, 12) and the sum of the speeds (20) must be in the same ratio, 3 to 5, as is the case.

Crossing the River
A Classic Puzzle by Henry Ernest Dudeney

During the Turkish stampede in Thrace, a small detachment found itself confronted by a wide and deep river. However, they discovered a boat in which two children were rowing about. It was so small that it would only carry the two children, or one grown person.How did the officer get himself and his 357 soldiers across the river and leave the two children finally in joint possession of their boat? And how many times need the boat pass from shore to shore?

Crossing the River
Solution

The two children row to the opposite shore. One gets out and the other brings the boat back. One soldier rows across; soldier gets out, and child returns with boat. Thus it takes four crossings to get one man across and the boat brought back. Hence it takes four times 358, or 1432 journeys, to get the officer and his 357 men across the river and the children left in joint possession of their boat.