Broken Bamboo

Geometry Level 2

A vertical 32-meter bamboo stick was broken by the wind, such that the tip meets the ground at a point 16 meters from the base. At what height above the ground (in meters) was it broken?


The answer is 12.

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15 solutions

Rahul Paswan
Jan 11, 2015

youu explain this question perfectly

Muzammil Hussain - 6 years, 4 months ago

Hi, I don't get why AC equals to A'C. I assumed that AB+A'C equals 32m

Anastasia Molko - 5 years, 5 months ago

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i also dont understand that

david umanskiy - 5 years, 4 months ago

Ac turn into A'C

Emran Hossain - 5 years, 4 months ago

The question was not phrased properly if you ask me

Ali Fah - 4 years, 1 month ago

Its the broken point of the bamboo. Its like you take a bamboo and break it at point C. So AC and A'C both are the same part of the bamboo. So we are just calling it with different names.

Abhijnan Saraswat Gogoi - 1 year, 2 months ago

me too, so got it wrong :\

I Love Brilliant - 11 months, 1 week ago

Nice question

Sonal Singh - 5 years, 5 months ago

Why is it squared

Michael Connolly - 4 years, 8 months ago

Can anyone explain the where "-64x" came from?

Emile Diaz de Leon - 4 years ago

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Expand (32-x)(32-x) = 32.32 -32x-32x + x.x = 1024-64x+x.x

Robert Oldroyd - 4 years ago

The wording of the problem is confusing. I believed the stick was 32 meters tall then the wind broke off segment AC so the remaining height of the stick would be 32-AC

Charles Andrews - 3 years, 8 months ago

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It looks like you interpreted the question correctly and you can certainly solve the problem using your proposed method. Notice that in Banti's diagram, the remaining height of the stick (x) is indeed 32 - AC. That is, x = 32 - (32-x)

If the height of the stick is 32-AC and the hypotenuse of the right triangle is AC then you'd use the Pythagorean theorem to get AC=20, which makes the height 32-20=12.

Adam Hoey - 3 years ago

This question was not phrased properly :(

Vaishnavi Venkataraghavan - 3 years, 4 months ago

I agree with a previous comment. The problem makes it sound like the stick was 32m BEFORE it broke. If worded correctly, this is simple.

Paul Koegler - 2 years, 5 months ago

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The stick was 32 meters before it broke. The drawing is a bit confusing but the question was clear.

Maureen Kimball - 2 years, 5 months ago

Hi, I don’t get why (32-x)^2 would equal x^2 + 16^2 / what that has to do with the problem. Wouldn’t it be as simple as, if it fall the length of 16ft , the part that fell would =16, therefore 32-16= 16, however that doesn’t make sense with the diagram?

Callie Tennyson - 2 years, 2 months ago
Ratnadip Kuri
Jan 12, 2015

Here, AC+BC=32

From triangle, A C 2 AC^2 - B C 2 BC^2 = A B 2 AB^2 = 1 6 2 16^2

\rightarrow (AC+BC) (AC-BC) = 256

\rightarrow 32 (AC-BC) = 256

\rightarrow AC-BC = 8

From above two equation we can calculate BC = 12

This is the one I employed

Tyrone Martinez-Black - 3 years, 5 months ago
Albert Wu
Jan 22, 2015

Set BC is x and AC is y, AC=A'C, so A'C =y x=32-y 16squared+xsquared=ysquared (pythagorean theorem) Then use x to find y 256+(32-y)squared=ysquared 256+1024-64y+ysquared=ysquared 256+1024=64y 1280=64y 20=y Then, 32-20=12

Well done Albert. One thing, to express 16 squared, you can write as 16^2. ^ is the standard way to express power. Keep up and Have fun.

Stanley Guo - 6 years, 4 months ago
Ahmed Obaiedallah
Jun 17, 2015

G i v e n \large \color{#3D99F6}Given

A B = 32 m \large AB=32 m

A B = 16 m \large A'B=16 m

L e t : A C = b , C B = a \large \color{#3D99F6}Let:\space AC=b, \space CB=a

T h e n : b = 32 a \large \color{#624F41}Then: \space b=32-a

A s s u m p t i o n : \large \color{#20A900}{Assumption}:\space the bamboo stick is perpendicular on the ground

U s i n g P y t h a g o r a s \large \color{#3D99F6}Using \space \color{#3D99F6}Pythagoras

b 2 = a 2 + 1 6 2 \large {\color{#D61F06}{b^2=a^2+16^2}}

( 32 a ) 2 = a 2 + 1 6 2 \large {(32-a)^2=a^2+16^2}

3 2 2 + a 2 2 × 32 a = a 2 + 1 6 2 \large {32^2+a^2-2\times32a=a^2+16^2}

2 10 2 6 a = 2 8 \large {2^{10}-2^6a=2^8}

a = 2 2 × 2 8 2 8 2 6 \large {\color{#D61F06}a=\Large\frac{2^2 \times 2^8 -2^8}{2^6}}

a = 2 8 × ( 2 2 1 ) 2 6 \large {\color{#D61F06}a=\Large\frac{2^8 \times (2^2-1)}{2^6}}

a = 2 8 6 × ( 2 2 1 ) = 4 × 3 = 12 m \large {\color{#D61F06}a=2^{8-6} \times (2^2-1)=4 \times 3=\boxed{\color{maroon}{12m}}}

William Isoroku
Jan 12, 2015

It's pretty easy to guess; since the distance 16 16 shown in the diagram is one of the legs of the right triangle, the triangle has to satisfy one of the Pythagorean triples (the answer has to be an integer). In this case, the triplets are 6 , 8 , 10 6,8,10 , multiplying by 2 gives 12 , 16 , 20 12,16,20

The answer is 12 \boxed{12}

Why is it required that the answer be an integer? Nowhere in the problem is that requirement stated. You got lucky that it happened to work out that way. Be careful about assumptions.

Matt Steele - 6 years, 4 months ago

Some times math is just a game , luck has a great deal with that. I like this solution

Alon Shikar - 4 years, 6 months ago

While it is not a requirement, the assumption that the solution may be related to a 3-4-5 triplet is easily checked. If 12 is the answer, then 20 must result from the hypotenuse for the total length to be 32. That is the case here. So what started as a guess ended up being verifiable rather quickly.

David Etter - 4 years, 6 months ago

lets x be the height above the ground,BC=x,AC=(32-x)A'C=(32-x), we have from right angle triangle x^2+16^2=(x-32)^2, by solving the above equation we get x=12

Let the distance from the base to the breaking point be x meter, hence the remaining is (32-x) meter. Therefore, the distance from the tip to the cracking point is equivalent to 32-x. This satisfies the phytagorean theorm of x^2+y^2=z^2. Substituting the hypothenuse with 32-x, adjacent side with x, and the other one with 16, thus we get x =12.

Freedom Li
May 9, 2021

I have figured out a formula. If the height of a bamboo is "h" and the distance between its root and the point at which its vertex touches, when broken, is "h\2". Then the formula for calculating the remaining height is: h(r) = 3h/8.

Let's check it. When h=32, then h(r) = 3*32/8 = 12.

My strategy: Calculating the total area ABA', the subtracting the area shaded blue. Calculating the line CB based on the remaining area.

Umesh Kamerikar
Jul 20, 2018

in pythagorus there is combination as 3,4,5 .in this they are multiply by 4,logical answer 12

David Andres
May 18, 2018

The question is asking as to resolve the length of BC

We know that AC = A´C, and from here we can create a couple of equations with two variables each to help us resolve the problem:

  • we know that AC + BC = 32;

  • according to Pythagoras theorem, AC2 = BC2 + 162 => AC2 - BC2 = 256. This can also be written as: (AC – BC) x (AC + BC) = 256;

We know from the first equation the value of AC + BC, which we can substiture in the second equation: (AC – BC) x 32 = 256 => AC – BC = 256 / 32 => AC – BC = 8

We have now ended up with two equations that are solved easily:

AC + BC = 32 and AC – BC = 8

Which takes us to conclude that BC = 12

Caesar Lopez Jr.
Nov 19, 2017

Using the 3 - 4 - 5 triangle, we find that 4 x 4 = 16, and thus that the other two are 3 x 4 = 12, and 5 x 4 = 20. Since we need the opposite side of the triangle, we fins that the answer is 12 meters

Relevant wiki: Pythagorean Theorem

Consider the diagram. Using pythagorean theorem , we have

( 32 x ) 2 = x 2 + 1 6 2 (32-x)^2=x^2+16^2

1024 64 x + x 2 = x 2 + 256 1024-64x+x^2=x^2+256

768 = 64 x 768=64x

x = 12 \boxed{x=12}

Peter Romero
Feb 17, 2017

From the problem:

B C + A C = 32 BC+AC=32

We can solve for A C AC :

A C = 32 B C AC=32-BC

From the Pythagorean Theorem:

A B 2 + B C 2 = A C 2 AB^2+BC^2=AC^2

Substituting in data from the problem we get:

1 6 2 + B C 2 = A C 2 16^2+BC^2=AC^2

256 + B C 2 = A C 2 \therefore256+BC^2=AC^2

Now we have two ways to express A C 2 AC^2

A C 2 = ( 32 B C ) 2 AC^2=(32-BC)^2

A C 2 = B C 2 + 256 AC^2=BC^2+256

so we can set those equal to each other and solve for B C BC .

( 32 B C ) 2 = B C 2 + 256 (32-BC)^2=BC^2+256

1024 64 B C + B C 2 = B C 2 + 256 \therefore 1024-64BC+BC^2=BC^2+256

1024 64 B C = 256 \therefore 1024-64BC=256

64 B C 768 \therefore -64BC-768

B C = 12 \therefore BC=12

Marina Hany
Mar 12, 2016

The no of squares in side cb = 5x The no of squares in side c a' = 8x By pathagorus Therefore, CB equal 12 cm

Paul Russo
Feb 15, 2016

I took the clever way out. The black lines dividing up the piece of bamboo look more or less even. So I counted them up (14 total). 32/14=2.28 .. 2.28 * 5 = 11.39 .. Round up .. Boom 12. ;)

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