1.

How much cardboard is required to make 35 penholders in the shape of cylinders, each of radius 3 cm and height 10.5 cm ?

Answer» Cardboard required to make 1 penholder
= (curved surface area + area of the base)
`= (2pi rh + pi r^(2)) cm^(2), " where " r = 3 cm and h = (21)/(2) cm`
`= pi r (2h + r) cm^(2) = {(22)/(7) xx 3 xx (2 xx (21)/(2) + 3)} cm^(2)`
`= ((22)/(7) xx 3 xx 24) cm^(2)`
Cardbaord required to make 35 penholders
`= ((22)/(7) xx 3 xx 24 xx 35) cm^(2) = 7920 cm^(2)`


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