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A succession of geometric shapes is obtained by dividing squares into smaller squares. The first three geometric shapes of these successions are illustrated as follows in the figure:

enter image description here

Considering that the largest square of each geometric shape has an area equal to one square meter, the area painted in black of the tenth geometric shape of this sequence, expressed in square meters, approximately, is equal to:

Attempt: Reason = $\frac{1}{2}$

Sides of squares = $\frac{1}{2}, \frac{1}{4}, \frac{1}{8},... \frac{1}{1024}$

tenth searched area = $(\frac{1}{1024})^2$

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  • $\begingroup$ Reason = $\frac12$ doesn't make sense to me. But your answer is right. $\endgroup$
    – Milten
    Commented Oct 13, 2021 at 22:03

2 Answers 2

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I am assuming that the "largest square" is the outer square, so that the first painted area corresponds to $0.25 \, m^2$.


$A(i) = \frac{1}{4} \; \text{for }i = 1$

$A(i) = \frac{1}{4} \cdot A(i-1) \; \text{for } i > 1$


$A(i) = {\left(\frac{1}{4}\right)}^i$

$A(10) = {\left(\frac{1}{4}\right)}^{10} = {\left(\frac{1}{1024}\right)}^2 = \boxed{\frac{1}{1048576} \, m^2} \approx 1 \, mm^2$

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It's right!

Then the answer should be $(\frac{1}{4})^{10} = \frac{1}{1048576}$

Note: I use $\frac{1}{4}$ straight away as the area.

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  • $\begingroup$ No, OP is correct. The first iteration is the one with $(\textrm{black area})=\frac14$. $\endgroup$
    – Milten
    Commented Oct 13, 2021 at 22:02

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