Square Inception

Geometry Level 1

The diagram above shows a large square, whose midpoints are connected up to form a smaller square. We then connect up the midpoints of the smaller square, to obtain the inner shaded square.

What fraction of the large square is shaded?

Note: Give your answer as a decimal to 2 decimal places.


The answer is 0.25.

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15 solutions

Abhinav Choudhary
Nov 29, 2014

Draw 2 diagonals in the bigger square:

We find 16 congruent triangles, of which 4 are shaded. So the answer is 4 16 = 1 4 = 0.25. \frac{4}{16} = \frac{1}{4} = 0.25.

We can also solve it by concepts of mid point....

Praveen Gautam - 4 years, 10 months ago

I solved it the really long way - working out side lengths using Pythagoras' Thereom. I then saw your wonderful solution and felt really bad ha. What a great way to solve it! Cheers :)

Harry Scully - 4 years, 7 months ago

I guessed and I was right.

Neil Dusheiko - 4 years, 7 months ago

I moved the square in my mind into a corner and estimated about a quart and got it right.

Caroline Co - 2 years, 5 months ago

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I did the same 😀😀

Kaustav Bhattacharya - 2 years, 4 months ago

I was correct, I just didn't know how they want to me to answer it.

CaveX Decode - 2 years, 3 months ago
Dawar Husain
Dec 16, 2014

Divide the figure into four parts. Appreciate the symmetry. (It's easy to see that the shaded square is has the same area as each of the four parts.) Thus, the answer is 1 4 = 0.25. \frac{1}{4} = 0.25.

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Sagar Jain
Nov 26, 2014

By Pythagoras theorem each square is half of the one around it. Hence , 1/2 x 1/2 = 1/4

How can you apply Pythagoras theorem????

Tejaswi Veginwar - 6 years, 6 months ago

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In response to @Tejaswi Veginwar The diagonal of each square is equal to the side of the square around it.

So, in the cause of the first two squares Side of the bigger square ( s ) (s) = ( d ) , (d), the diagonal of the smaller one. By the Pythagorean Theorem , d 2 = s 2 + s 2 , d^2 = s^2+s^2, so d = 2 s 2 . d=\sqrt{2s^2}.

Therefore, the area of the bigger square is 2 s 2 , 2s^2, and the area of the smaller square is s 2 , s^2, for a ratio of 1:2. Similarly for the smaller square and the shaded square we get ratio of 1:2

So finally, ratio between shaded square and bigger square is 1 2 × 1 2 = 1 4 = 0.25. \frac{1}{2} \times \frac{1}{2} = \frac{1}{4} =0.25.

Sagar Jain - 6 years, 6 months ago

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the correct answer is 2 \times 3 2^{34} a {i-1} \frac{2}{3} \sqrt{2} \sum {i=1}^3 \sin \theta \boxed{123}

Remzy Yimam - 5 years, 6 months ago

InCorrect the Ans in 1/2 . Draw 2 perpendicular there will be 4 Triangles inside all the Triangles inside have the same area, and hence its 1/2 and not 1/4

Sunil Paryani - 6 years, 6 months ago

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@Sunil Paryani Are you silly?It's said the area,not the side length.

Phạm Hoàng - 2 years, 11 months ago

yes,i agree it may b a parallelogram..

Amrita Singanjude - 6 years, 6 months ago

InCorrect the Ans in 1/2 . Draw 2 perpendicular there will be 4 Triangles inside all the Triangles inside have the same area, and hence its 1/2 and not 1/4

Sunil Paryani - 6 years, 6 months ago

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the side length is 1/2 that of the full square but the area is actually 1/4

Brett Hartley - 6 years, 6 months ago

Let me explain with example, Take a Square shape paper and fold the paper as shown in the diagram, On first step, Folding the four corners will cover half of the page. similarly, the second fold will cover half of the remaining, thus 1/4 is covered (Shaded)

Meeran Mydeen - 6 years, 6 months ago

The problem ask for fraction of the shaded area to the whole square and not the fraction of the shaded to the unshaded part.

Billy John Mendiola - 6 years, 5 months ago
Robert Haywood
Nov 27, 2014

This one was quite hard for me, considering that there was nothing explicitly stating that any of those figures are squares. Eventually, I gave up and assumed that that is what they were. Now, to the problem itself:

s 1 s_1 is the side length of the first square.

s 2 s_2 is for the second square.

s 3 s_3 is the third.

The length of one side of the second square is obviously equal to a diagonal in the first (Imagine making the diagonal, and sliding it down to the side of the second square) The diagonal of a square is equal to s 2 s\sqrt{2} , since it creates a 45-45-90 right triangle, and the diagonal is the hypotenuse, so then s 1 2 = s 2 s_1\sqrt{2}=s_2 . By that same logic, s 2 2 = s 3 s_2\sqrt{2}=s_3 .

Assume s 1 = 1 s_1=1 . Plugging that into our equations, that would mean s 2 = 2 s_2=\sqrt{2} , and s 3 = 2 s_3=2 .

a 1 a_1 is the area of the first square.

a 2 a_2 is for the second square.

a 3 a_3 is the third.

Using the corresponding side lengths, we can conclude:

a 1 = 1 a_1=1

a 2 = 2 a_2=2

a 3 = 4 a_3=4

Say we shade a 2 a_2 . Then, the fraction of the diagram that is shaded is a 2 a 3 = 2 4 = 1 2 \frac{a_2}{a_3}=\frac{2}{4}=\frac{1}{2} . The fraction of a 2 a_2 that is shaded by a 1 a_1 is equal to a 1 a 2 = 1 2 \frac{a_1}{a_2}=\frac{1}{2} .

Therefore, in order to get the amount of a 3 a_3 that a 1 a_1 takes up, we multiply a 2 a 3 a 1 a 2 = 1 2 1 2 = 1 2 2 = 1 4 = 0.25 \frac{a_2}{a_3}*\frac{a_1}{a_2}=\frac{1}{2}*\frac{1}{2}=\frac{1}{2*2}=\frac{1}{4}=0.25

Therefore, our answer is 0.25 \boxed{0.25} !

InCorrect the Ans in 1/2 . Draw 2 perpendicular there will be 4 Triangles inside all the Triangles inside have the same area, and hence its 1/2 and not 1/4

Sunil Paryani - 6 years, 6 months ago

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Yes, you would be correct. Great job, man! You just proved... What is it? 816 people wrong! I applaud you! I mean, your logic is SO sound, and I totally agree with you, the answer is DEFINITELY 1 2 \frac{1}{2} ...

Except that that only applies if there are TWO squares in total, and there are 3.

Since you obviously didn't read my solution, I created two equations- one for the lopsided, middle square in relation to the gigantic, third one, and another for the small, shaded square in relation to the lopsided, middle one. We then can find the ratio of the small one to the gigantic one:

( 1 : 2 ) : 2 = 1 2 : 2 = 1 2 2 = 1 2 1 2 = 1 1 2 2 = 1 4 = 0.25 (1:2):2=\frac{1}{2}:2=\frac{\frac{1}{2}}{2}=\frac{1}{2}*\frac{1}{2}=\frac{1*1}{2*2}=\frac{1}{4}=\boxed{0.25} .

Hence it's 1 4 \frac{1}{4} and not 1 2 \frac{1}{2} .

Robert Haywood - 6 years, 6 months ago

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oops sry mate... Plz dont get angry it was a silly mistake .. :)

Sunil Paryani - 6 years, 6 months ago
Manuj Dagar
Nov 27, 2014

Easy one is mid point theorem.If we join all the mid points of a square,then the square obtained has area equal to half of the bigger one.

Yuki Kuriyama
Sep 7, 2015

Considering the bigger square,take its each side as 2a..(i.e, a+a) & start solving.

Fedor Panafidin
Oct 19, 2015

SIMPLE SOLUTION

Let 1 triangle of the second largest square be a 1, now you can easily deduct that the area of the shaded square is 4. The area of one of the triangles of the largest square is then 2. (2+1)*4 + 4 = 16 So, 4/16 = 1/4 = 0.25

P.S. Thank you for reading.

Amal Lukose
Jul 16, 2015

For this we just need a little common sense the area of the square inside is half of the first similar in nest case so half of half is quarter

ROBERT HAYWOOD: (por error de la página figura en todas las soluciones presentadas, no fui yo el responsable)... Sorry.

Mucho trabajo innecesario. Que razón tiene para multiplicar la relación de las áreas para llegar a la respuesta. Simplificando este producto llega a la respuesra. El resultado se obtiene con la relación a3/a1 = L3/L1. Muy complicado su trabajo!

Jaime Maldonado - 5 years, 7 months ago

Consider my diagram. Using the pythagorean theorem, we have

y = x 2 + x 2 = x 2 y=\sqrt{x^2+x^2}=x\sqrt{2}

It follows that y 2 = x 2 2 \dfrac{y}{2}=\dfrac{x\sqrt{2}}{2} .

Use pythagorean theorem again.

z = ( y 2 ) 2 + ( y 2 ) 2 = ( x 2 2 ) 2 + ( x 2 2 ) 2 = x z=\sqrt{\left(\dfrac{y}{2}\right)^2+\left(\dfrac{y}{2}\right)^2}=\sqrt{\left(\dfrac{x\sqrt{2}}{2}\right)^2+\left(\dfrac{x\sqrt{2}}{2}\right)^2}=x

The ratio of their areas is

A 1 A 2 = x 2 ( 2 x ) 2 = x 2 4 x 2 = 1 4 = \dfrac{A_1}{A_2}=\dfrac{x^2}{(2x)^2}=\dfrac{x^2}{4x^2}=\dfrac{1}{4}= 0.25 \boxed{0.25}

Christian König
Jun 4, 2016

You can shift the shaded square to the top left (or every other) corner of the biggest square. And while doing so, you see that the corners of the shaded square are moving parallel along on two sides of the diagonal square. Since the corners of this diagonal square mark the midpoint of the biggest square's sides, the sidelength of the shaded square is half of the sidelength of the biggest square. Therefore the areas ratio is 1:4.

Vishal Verma
May 25, 2016

Draw 2 diagonals in the bigger square We find 16 congruent triangles,in which 4 are shaded. So, 4/16 =1/4 =0.25

Raakin Kabir
Apr 30, 2016

Since I didn't have any other way to solve the problem, I solved the problem by plugging in values for the squares. So.....

I plugged in that the outer square had an area of 64 square units, thus an 8 by 8 square.

The second one would have a diagonal length of 8 because the diagonal stretches as far as the bigger squares side length.

I found out that from the edge of the square to the center of the smallest square is 4.

That means that the smaller square has an "edge to center" length of 2.

That means that the side length of the smallest square is 4 and 4 * 4 is equal to 16.

Bigger square area: 64 Smaller square area: 16

16/64 = 0.25 So the answer is 0.25

Ch Chen
Mar 28, 2016

http://ppt.cc/b5Dqt

See the url for the picture that has the supporting line (red) that explain the answer very easily. Calculation: (shaded area / largest square area) = 4/16 = 0.25

Judit Coll
Aug 2, 2015

I tried to input 1/4 and coud not, when I was asked to write a number. But 1/4 is the way I use to write fractions. Then I tried with 4 (meaning 4th part), but that is obviously a wrong answer. I suggest adding the possibility to write fractions. Numbers like 1/3, for instance, cannot be written in a decimal form.

Nilambu Banik
Jul 28, 2015

In which angle this problem has been reported??? :-o

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