In the following diagram, the side length of the square is equal to 4 .

At π = 3.14, what is the gray shaded area subtracting from it the dark shaded area ?

The answer is 0.3.

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The grey area at each corner is $\frac{1}{4}(4-\pi)$

The black area is $\pi - 4\frac{1}{4}(4 - \pi)$

Total area of grey area minus black area is

$12(\frac{1}{4}(4-\pi)) - (\pi - 4\frac{1}{4}(4 - \pi)) = 16 - 5\pi$

which, if $\pi = 3.14$ , works out to exactly $0.3$