If the height of a cylinder is 20cm minus 5cm, the surface area of the cylinder will be reduced by 31.4cm?

31.4 △ 5 = 6.28 ------ perimeter of bottom surface
6.28 ﹣ 3.14 ﹣ 2 = 1 - bottom radius
6.28 * 20 = 125.6 square centimeter - side area
3.14 * 1 * 1 * 2 = 6.28 - area of two bottom surfaces
Surface area: 125.6 + 6.28 = 131.88 (cm2)

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