Question 174449
A cylinder with a diamter of 10 centimeters and a height of 20 centimeters is cut in 1/2 horizontally. What is the difference between the combined total surface areas of the 2 newly created cylinders and the total surface area of the original cylinder?
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Ignoring the width of the cut (it can be zero in a math problem):
The difference is the area of 2x the cross-sectional area of the cylinder.  Two (2) new circular areas are created, so 2*pi*r^2 is added to the total surface area.
That is the difference, before and after:  2*pi*r^2 = 2*pi*5^2
= 50pi sq cms
=~ 157 sq cms