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The perimeter of the rectangle ABCD is 30 cm. Three other rectangles are placed so that their centres are at the points A, B, D. The sum of their perimeters is 20 cm. What is the total length of the thick line?
A 50 cm
B 45 cm
C 40 cm
D 35 cm
E impossible to determine

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The website was created in September 2005.

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It is visited by 14,000 - 28,000 people daily, mostly from USA, Bulgaria, Russia, India, Philippines, Ukraine, Serbia...

In 2011 was created a Russian version, and in 2015 Serbian.