1995 AIME Problems/Problem 1

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Problem

Square $\displaystyle S_{1}$ is $1\times 1.$ For $i\ge 1,$ the lengths of the sides of square $\displaystyle S_{i+1}$ are half the lengths of the sides of square $\displaystyle S_{i},$ two adjacent sides of square $\displaystyle S_{i}$ are perpendicular bisectors of two adjacent sides of square $\displaystyle S_{i+1},$ and the other two sides of square $\displaystyle S_{i+1},$ are the perpendicular bisectors of two adjacent sides of square $\displaystyle S_{i+2}.$ The total area enclosed by at least one of $\displaystyle S_{1}, S_{2}, S_{3}, S_{4}, S_{5}$ can be written in the form $\displaystyle m/n,$ where $\displaystyle m$ and $\displaystyle n$ are relatively prime positive integers. Find $\displaystyle m-n.$

AIME 1995 Problem 1.png

Solution

The sum of the areas of the squares if they were not interconnected is a geometric sequence: $1^2 + (\frac{1}{2})^2 + \1dots + (\frac{1}{16})^2$ (Error compiling LaTeX. Unknown error_msg). Then subtract the areas of the intersections: $(\frac{1}{4})^2 + \1dots + (\frac{1}{32})^2$ (Error compiling LaTeX. Unknown error_msg). The majority of the terms cancel, leaving $1 + \frac{1}{4} - \frac{1}{1024}$, which simplifies down to $\frac{1024 + (256 - 1)}{1024}$. Thus, $m-n =  255$.

Alternatively, take the area of the first square and add $\frac{3}{4}$ of the areas of the remaining squares. This results in $1 + \frac{3}{4}(\frac{1}{2}^2 + \1dots + \frac{1}{16}^2)$ (Error compiling LaTeX. Unknown error_msg), which when simplified will produce the same answer.

See also

1995 AIME (ProblemsAnswer KeyResources)
Preceded by
First Question
Followed by
Problem 2
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
All AIME Problems and Solutions