Squares all around

Geometry Level 1

In the above rectangle, all the smaller shapes are squares. If the two green squares in the center each have a side length of 1, what is the area of the rectangle?

40 88 130 104

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8 solutions

Brock Brown
Mar 27, 2015

Why not prove it with a gif?

Let A A be the total area.

fibonacci fibonacci A = 8 × ( 8 + 5 ) = 104 \implies A = 8 \times (8+5)=\boxed{104}

Nice Gif!!!!

Chung Kevin - 6 years, 2 months ago

oh what a answer

Mohammad Babar - 6 years, 2 months ago

nice solution!

A Former Brilliant Member - 3 years, 12 months ago
Pi Han Goh
Mar 26, 2015

Fibonacci squares comes to mind.

Denoting the length of green squares as F 1 , F 2 F_1, F_2 , the brown square: F 3 F_3 , blue square: F 4 F_4 , purple square: F 5 F_5 , red square: F 6 F_6 . So the answer is simply ( F 6 + F 5 ) × ( F 5 + F 4 ) = F 7 × F 6 = 13 × 8 = 104 (F_6 + F_5 ) \times ( F_5 + F_4 ) = F_7 \times F_6 = 13 \times 8 = \boxed{104} .

The generalization is: for a total of n n squares used in the Fibonacci squares, the area is F n + 1 F n F_{n+1} F_n (thus proving the identity k = 1 n F k 2 = F n + 1 F n \displaystyle \sum_{k=1}^n F_k ^2 = F_{n+1} F_n geometrically).

Great solution

Mir Tushar - 6 years, 2 months ago
Mohammed Ali
Mar 31, 2015

Use Fibonacci Sequence 0, 1, 1, 2, 3, 5, 8

Nice observation :)

Aman Sharma - 6 years, 2 months ago

The first number of the Fibonacci sequence is 1, not 0 though :-)

Nicolai Kofoed - 5 years, 5 months ago

We want to find the area of the entire rectangle.

Side of Red Square X (Side of Red Square + Side of Purple Square)

We know that the green squares are each 1 and that the orange square must have a side length of 2.

Then, the Blue must have Green + Orange, or 3.

Purple is 2Green + Blue = 5

Red is Orange + Green + Purple = 8

So going back to our first equation,

WE replace into this Side of Red Square X (Side of Red Square + Side of Purple Square)

To get: 8 X (8+5) = 8 X 13 = 104

Good approach. Keep it up!

Chung Kevin - 6 years, 2 months ago

Really good explanation. Hats Off!

Ashish Garg - 6 years, 2 months ago
Marvin Kalngan
Apr 30, 2020

I calculated mentally.

This is a piece of ice cream. Just draw a diagram and label the sides correctly. Drawing the correct diagram is half of the solution.

Chockalingam S
Mar 28, 2015

Fibonacci explained :). Answer is 104

Suyog Salgaonkar
Mar 27, 2015

Green 1, orange2, blue3, purple5, red8 so 8*13=104

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