Henry Ernest Dudeney/Puzzles and Curious Problems/Geometrical Problems/Various Geometrical Puzzles
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Henry Ernest Dudeney: Puzzles and Curious Problems: Geometrical Problems: Various Geometrical Puzzles
$200$ - Measuring the River
- A traveller reaches a river at the point $A$,
- and wishes to know the width across to $B$.
- As he has no means of crossing the river, what is the easiest way of finding its width?
$201$ - Square and Triangle
- Take a perfectly square piece of paper,
- and fold it as to form the largest possible equilateral triangle.
- A triangle in which the sides are the same length as those of the square, as shown in our diagram,
- will not be the largest possible.
- Of course, no markings or measurements may be made except by the creases themselves.
$202$ - A Garden Puzzle
- What is the area?
$203$ - A Triangle Puzzle
- In the solution to our puzzle No. $162$, we said that:
- "there is an infinite number of rational triangles composed of three consecutive numbers like $3$, $4$, $5$, and $13$, $14$, $15$."
- We here show these two triangles.
- In the first case the area ($6$) is half of $3 \times 4$,
- It will be found interesting to discover such a triangle with the smallest possible three consecutive numbers for its sides,
- that has an area that may be exactly divided by $20$ without remainder.
$204$ - The Donjon Keep Window
- In The Canterbury Puzzles Sir Hugh de Fortibus calls his chief builder, and, pointing to a window, says:
- See our Figure $A$.
- "I desire that another window be made higher up,
- whose four sides shall also be each one foot,
- but it shall be divided by bars into eight lights, whose sides shall be all equal."
- This the craftsman was unable to do, so Sir Hugh showed him our Figure $B$, which is quite correct.
- But he added, "I did not tell thee that the window must be square, as it is most certain it never could be."
- Now, an ingenious correspondent, Mr. George Plant, found a flaw in Sir Hugh's conditions.
- Something that was understood is not actually stated,
- and the window may, as the conditions stand, be perfectly square.
- How is it to be done?
$205$ - The Square Window
- A man had a window a yard square, and it let in too much light.
- He blocked up one half of it, and still had a square window a yard high and a yard wide.
- How did he do it??
$206$ - The Triangular Plantation
- A man had a plantation of twenty-one trees set out in the triangular form shown in the diagram.
- If he wished to enclose a triangular piece of ground with a tree at each of the three angles,
- how may different ways of doing it are there from which he might select?
- The dotted lines show three ways of doing it.
- How many are there altogether?
$207$ - Six Straight Fences
- A man had a small plantation of $36$ trees, planted in the form of a square.
- Some of these died, and had to be cut down in the positions indicated by crosses in the diagram.
- How is it possible to put up $6$ straight fences across the field,
- so that every one of the remaining $20$ trees shall be in a separate enclosure?
- As a matter of fact, $22$ trees might be so enclosed by $6$ straight fences if their positions were a little more accommodating,
- but we have to deal with the trees as they stand in regular formation, which makes all the difference.
$208$ - Dividing the Board
- A man had a board measuring $10$ feet in length, $6$ inches wide at one end, and $12$ inches wide at the other,
- as shown in the diagram.
- How far from $B$ must the straight cut at $A$ be made in order to divide it into two equal pieces?
$209$ - A Running Puzzle
- $ABCD$ is a square field of $40$ acres.
- The line $BE$ is a straight path, and $E$ is $110$ yards from $D$.
- In a race Adams runs direct from $A$ to $D$,
- but Brown has to start from $B$, go from $B$ to $E$, and thence to $D$.
- Each keeps to a uniform speed throughout, and when Brown reaches $E$, Adams is $30$ yards ahead of him.
- Who wins the race, and by how much?
$210$ - Pat and his Pig
- The diagram represents a field $100$ yards square.
- Pat is at $A$ and his pig is at $B$.
- The pig runs straight for the gateway at $C$.
- As Pat can run twice as fast as the pig, you would expect that he would first make straight for the gate and close it.
- But this is not Pat's way of doing things.
- He goes directly for the pig all the time, thus taking a curved course.
- Now, does the pig escape, or does Pat catch it?
- And if he catches it, exactly how far does the pig run?
$211$ - The Twenty Matches
- The diagram shows how $20$ matches, divided into two groups of $14$ and $6$,
- may form two enclosures so that one space enclosed is exactly $3$ times as large as the other.
- Now divide the $20$ matches into two groups of $13$ and $7$,
- and with them again make two enclosures,
- one exactly three times as large as the other.
$212$ - Transplanting the Trees
- A man has a plantation of $22$ trees arranged in the manner shown.
- How is he to transplant only six of the trees so that they shall then form $20$ rows with $4$ trees in every row?.
$213$ - A Swastikaland Map
- Swastikaland is divided in the manner shown in our illustration.
- The Lord High Keeper of the Maps was ordered so to colour this map of the country
- that there should be a different colour on each side of every boundary line.
- What was the smallest number of colours that he required?
$214$ - Colouring the Map
- Colonel Crackham asked his young son one morning to colour all the $26$ districts in this map
- in such a way that no two contiguous districts should be the same colour.
- The lad looked at it for a moment, and replied,
- "I haven't enough colours by one in my box."
- This was found to be correct.
- How many colours had he?
- He was not allowed to use black or white -- only colours.
$215$ - The Damaged Rug
- A lady had a valuable Persian rug, $12$ feet by $9$ feet, which was badly damaged by fire.
- So she cut from the middle a strip $8$ feet by $1$ foot, as shown in the diagram,
- How did she do it?
$216$ - The Four Householders
- The diagram represents a square plot of land with four houses, four trees, a well (W) in the centre,
- and hedges planted across with four gateways.
- can you divide the ground so that each householder shall have an equal portion of land,
- one tree, one gateway, an equal length of hedge, and free access to the well without trespass?
$217$ - The Three Fences
- A man had a circular field, and he wished to divide it into four equal parts by three fences, each of the same length.
- How might this be done?
$218$ - The Farmer's Sons
- A farmer once had a square piece of ground on which stood $24$ trees, exactly as shown in the illustration.
- He left instructions in his will that each of his eight sons should receive the same amount of ground and the same number of trees.
- How was the land to be divided in the simplest possible manner?
$219$ - The Three Tablecloths
- A person had $3$ tablecloths, each $4$ feet square.
- What is the length of the side of the largest square table top that they will cover together?
$220$ - The Five Fences
- A man owned a large, fenced-in field in which were $16$ oak trees, as depicted in the diagram.
- He wished to put up five straight fences so that every tree should be in a separate enclosure.
- How did he do it?
$221$ - The Fly's Journey
- A fly, starting from point $A$, can crawl around the four sides of the base of this cubical block in $4$ minutes.
- Can you say how long it will take to crawl from $A$ to the opposite corner $B$?
$222$ - Folding a Pentagon
- Given a ribbon of paper, as in the diagram, of any length -- say more than $4$ times as long as broad --
- it can all be folded into a perfect pentagon,
- with every part lying within the boundaries of the figure.
- The only condition is that the angle $ABC$ must be the correct angle of two contiguous sides of a regular pentagon.
- How are you to fold it?
$223$ - The Tower of Pisa
- Suppose you were on the top of the Tower of Pisa, at a point where it leans exactly $179$ feet above the ground.
- Suppose you were to drop an elastic ball from there such that on each rebound it rose exactly one-tenth of the height from which it fell.
- What distance would the ball travel before it came to rest?
$224$ - The Tank Puzzle
- The area of the floor of a tank is $6$ square feet,
- $(1)$ How much does the water rise if a $1$ foot metal cube is put in it,
- $(2)$ How much farther does it rise if another cube like it is put in by its side?
$225$ - An Artist's Puzzle
- An artist wished to obtain a canvas for a painting which would allow for
- the picture itself occupying $72$ square inches,
- a margin of $4$ inches on top and on bottom,
- and $2$ inches on each side.
- What is the smallest dimensions possible for such a canvas?
$226$ - The Circulating Motor-Car
- A car was running on a circular track such that the outside wheels were going twice as fast as the inside ones.
- What was the length of the circumference described by the outer wheels?
- The wheels were $5$ feet apart at the axle-tree.
$227$ - A Match-Boarding Order
- A man gave an order for $297$ feet of match-boarding of usual width and thickness.
- There were to be $16$ pieces, all measuring an exact number of feet -- no fractions of a foot.
- He required $8$ pieces of the greatest length, the remaining pieces to be $1$ foot, $2$ feet, or $3$ feet shorter than the greatest length.
- How was the order carried out?
$228$ - The Ladder
- A ladder was fastened on end against a high wall of a building.
- It was unfastened and pulled out $4$ yards at the bottom.
- It was then found that the ladder had descended just one-fifth of the length of the ladder.
- What was the length of the ladder?
$229$ - Geometrical Progression
- Write out a series of whole numbers in geometrical progression, starting from $1$,
- so that the numbers should add up to a square.
- Thus, $1 + 2 + 4 + 8 + 16 + 32 = 63$.
- But this is one short of being a square.
$230$ - In a Garden
- Consider a rectangular flower-bed.
- If it were $2$ feet broader and $3$ feet longer, it would have been $64$ square feet larger;
- if it were $3$ feet broader and $2$ feet longer, it would have been $68$ square feet larger.
$231$ - The Rose Garden
- A man has a rectangular garden, and wants to make exactly half of it into a large bed of roses,
- with a gravel path of uniform width round it.
- Can you find a general rule that will apply equally to any rectangular garden, whatever its proportions?
$232$ - A Pavement Puzzle
- Two square floors had to be paved with stones each $1$ foot square.
- The number of stones in both together was $2120$, but each side of one floor was $12$ feet more than each side of the other floor.
- What were the dimensions of the two floors?
$233$ - The Nougat Puzzle
- A block of nougat is $16$ inches long, $8$ inches wide, and $7 \tfrac 1 2$ inches deep.
- What is the greatest number of pieces that I can cut from it measuring $5$ inches by $3$ inches by $2 \tfrac 1 2$ inches?
$234$ - Pile Driving
- During some bridge-building operations a pile was being driven into the bed of the river.
- A foreman remarked that at high water a quarter of the pile was embedded in the mud,
- What was the length of the pile?
$235$ - An Easter Egg Problem
- I have an easter egg exactly $3$ inches in length, and $3$ other eggs all similar in shape,
- having together the same contents as the large egg.
- Can you tell me the exact measurements for the lengths of the three smaller ones?
$236$ - The Pedestal Puzzle
- A man had a block of wood measuring $3$ feet by $1$ foot by $1$ foot,
- which he gave to a wood-turner with instructions to turn from it a pedestal,
- saying that he would pay him a certain sum for every cubic inch of wood taken from the block in the process of turning.
- The ingenious turner weighed the block and found it to contain $30$ pounds.
- After he had finished the pedestal it was again weighed, and found to contain $20$ pounds.
- As the original block contained $3$ cubic feet, and it had lost just one-third of its weight,
- the turner asked payment for $1$ cubic foot.
- But the gentleman objected, saying that the heart of the wood might be heavier or lighter than the outside.
- How did the ingenious turned contrive to convince his customer that he had taken not more and not less than $1$ cubic foot from the block?
$237$ - The Mudbury War Memorial
- The inhabitants of Mudbury recently erected a war memorial,
- and they proposed to enclose a piece of ground on which it stands with posts.
- They found that if they set up the posts $1$ foot asunder they would have too few by $150$.
- But if they placed them a yard asunder there would be too many by $70$.
- How many posts had they in hand?
$238$ - A Maypole Puzzle
- During a gale a maypole was broken in such a manner that it struck the level ground at a distance of $20$ feet from the base of the pole,
- where it entered the earth.
- It was repaired, and broken by the wind a second time at a point $5$ feet lower down,
- and struck the ground at a distance of $30$ feet from the base.
- What was the original height of the pole?
$239$ - The Bell Rope
- A bell rope, passing through the ceiling above, just touches the belfry floor,
- How long was the rope from floor to ceiling?
$240$ - Counting the Triangles
- Draw a pentagon, and connect each point with every other point with straight lines, as in the diagram.
- How many different triangles are contained in this figure?
$241$ - A Hurdles Puzzle
- The answers given in the old books to some of the best-known puzzles are often clearly wrong.
- Yet nobody ever seems to detect their faults.
- Here is an example.
- A farmer had a pen made of fifty hurdles, capable of holding a hundred sheep only.
- Supposing he wanted to make it sufficiently large to hold double that number, how many additional hurdles must he have?
$242$ - Correcting a Blunder
- Mathematics is an exact science, but first-class mathematicians are apt, like the rest of humanity, to err badly on occasions.
- On referring to Peter Barlow's Elementary Investigation of the Theory of Numbers, we hit on this problem:
- "To find a triangle such that its three sides, perpendicular, and the line drawn from one of the angles bisecting the base
- may all be expressed in rational numbers."
- "To find a triangle such that its three sides, perpendicular, and the line drawn from one of the angles bisecting the base
- He gives as his answer the triangle $480$, $299$, $209$, which is wrong and entirely unintelligible.
- Readers may like to find a correct solution when we say that all the five measurements may be in whole numbers,
- and every one of them less than a hundred.
- It is apparently intended that the triangle must not itself be right-angled.
$243$ - The Squirrel's Climb
- A squirrel goes spirally up a cylindrical post, making the circuit in $4$ feet.
- How many feet does it travel to the top if the post is $16$ feet high and $3$ feet in circumference?
$244$ - Sharing a Grindstone
- Three men bought a grindstone $20$ inches in diameter.
- How much must each grind off so as to share the stone equally,
- making an allowance of $4$ inches off the diameter as waste for the aperture?
- We are not concerned with the unequal value of the shares for practical use --
- only with the actual equal quantity of stone each receives.