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You are right. I made a foolish mistake by considering the radius as the diameter in the first step.
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Bunuel

In the figure above, the centers of four equal circles lie along the diameter of the large circle. If the circumference of the large circle is 64π, what is the area of the shaded region?

A. 16π
B. 32π
C. 64π
D. 128π
E. 256π

Attachment:
2016-01-31_1804.png

Circumference of Larger Circle = πD = 64π
i.e. Diameter, D = 64
i.e. iameter of smaller circle, d = D/4 = 64/4=16
Radius of smaller circle = 16/2 = 8

Area of 4 smaller circles = 4*π*r^2 = 4*π*8^2 = 256π

Answer: Option E
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Vyshak
2*pi*r = 64*pi
r = 32

d1 + d2 + d3 + d4 = 32
Since d1 = d2 = d3 = d4; 4d1 = 32
d1 = 8
d1 = 2r1
r1 = 4

Area of one shaded circle = pi*(4^2) = 16pi
Area of four shaded circles = 4*16pi = 64pi

Answer: C

The highlighted step above is incorrect


The correct equation should be d1 + d2 + d3 + d4 = Diameter of bigger circle = 64
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R must be 32
since we have 4 smaller circles, R of each of them must be equal to 32/4 = 8.
area is pi*r^2.
64pi is area of a small circle
area of 4 small circles =64*4 or 128*2 or 256pi.

E.
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