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Chapter 13 Class 9 Surface Areas and Volumes

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Last updated at March 22, 2023 by Teachoo

Ex 13.2, 11 The students of a Vidyalaya were asked to participate in a competition for making and decorating penholders in the shape of a cylinder with a base, using cardboard. Each penholder was to be of radius 3 cm and height 10.5 cm. The Vidyalaya was to supply the competitors with cardboard. If there were 35 competitors, how much cardboard was required to be bought for the competition? [ = 22/7] Here the pen holder is open at the top, but covered at the bottom Surface area of 1 penholder = Curved Surface area of cylinder with + Area of bottom circle with radius 3 cm Radius (r) of the circular end of cylindrical penholder = 3 cm Height (h) of penholder = 10.5 cm Surface area of 1 penholder = Curved Surface area of cylinder with + Area of circle with radius 3 cm = 2 rh + r2 = (2 22/7 3 10.5+22/7 (3)2) cm2 = (22/7 (2 3 10.5+(3)2)) cm2 = (22/7 (63+9)) cm2 = (22/7(72)) cm2 Area of cardboard required = Surface area of 35 penholder = 35 (22/7 " " 72) cm2 = 5 (22" " 72) cm2 = 7920 cm2 Therefore, 7920 cm2 cardboard sheet will be bought.