To infinity and beyond

Geometry Level 2

The given figure shows a square of side 10 units. Joining the midpoints of its sides, another square is drawn in it.

This process is continued forever.

What is the sum of areas of all the squares?

150 200 100 \infty

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5 solutions

If you observe the figure properly , you can see that the area of each \text{If you observe the figure properly , you can see that the area of each } square is 1/2 times of the area of the previous square. \text{square is 1/2 times of the area of the previous square.}

Let area of the larger square be A \text{Let area of the larger square be A}

Clearly the sum of the areas will be a GP like this : \text{Clearly the sum of the areas will be a GP like this : }

S + S 2 + S 4 + . . . . . S+\frac{S}{2}+\frac{S}{4}+.....

i.e, \text{i.e,}

S × ( 1 + 1 2 + 1 4 + . . . . . ) S \times (1+\frac{1}{2}+\frac{1}{4}+.....)

Now, the formula for infinite series of GP can be used \text{Now, the formula for infinite series of GP can be used }

S × 1 1 1 2 S\times\frac{1}{1-\frac{1}{2}}

Which is nothing but , \text{Which is nothing but ,}

2 × S 2\times S

Area of larger square S is, \text{Area of larger square S is,}

S = 10 × 10 = 100 S = 10\times 10 = 100

Sum of the area of all the squares is, \therefore \text{Sum of the area of all the squares is,}

2 × 100 = 200 2\times 100 = \boxed{200}

Are all these figures meant to be drawn to scale? I deliberately avoided that assumption...

Jeffrey Li - 5 years, 9 months ago
Akshat Sharda
Jul 25, 2015

Hint: Its a G.P.(Geometric Progression).

Use sum = a 1 r =\frac{a}{1-r}

Where:

a a = first term of your GP.

r r = common ratio.

Yes, an INFINITE GP

Aakash Khandelwal - 5 years, 10 months ago

That's right. Just the area *(1+1/2+.........1/2^{n} )

Juan Rodriguez - 5 years, 10 months ago
Geo Ferrolino
Jul 30, 2015

For every succeeding side, you divide that side by sq. root of 2. Therefore, from 10, next side will be 10/(sq. of 2), then 5, then so on. If the ratio for each side is sq. of 2 and the formula for the equation of a square is s^2, then the ratio for its succeeding area is 1/(sq. of 2)^2, or simply 1/2. So, the first area is 100, then 50, 25, so on. Using the formula for infinite geometric series,

S = A1 / 1-r

S = 100 / 1-(1/2)

S = 200

Simon Reichert
Sep 4, 2015

The next square has half the area of the previous one. We get the geometric series (with limit 2) times 100. Hence, the absolute area is 200.

Hadia Qadir
Jul 29, 2015

It is 200 square units. The first square area is 10*10 = 100 square unit. The inner square of a square is a half size of the square. If you use a second piece of paper, cut it and keep a half, then cut the other half... continue doing it until you can no longer cut it in half, you would have the whole second piece of paper. Thus, the sum of the areas of all the squares is 200 square units.

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