How to find the perimeter of a square - GRE Quantitative Reasoning

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Question

Semicirclesquare

The diagram above represents a square ABCD with a semi-circle directly attached to its side. If the area of the figure is 16 + 2π, what is its outer perimeter?

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Answer

We know that our area can be represented by the following equation:

Instead of solving the algebra, you should immediately note several things. 16 = 42 and 4 = 22. If the side of the square is 4, then s = 4 would work out as:

which is just what we need.

With s = 4, we know that 3 sides of our figure will have a perimeter of 12. The remaining semicircle will be one half of the circumference of a circle with diameter of 4; therefore it will be 0.5 * 4 * π or 2π.

Therefore, the outer perimeter of our figure is 12 + 2π.

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