NCERT Solutions for Class 9 Maths Chapter 13
Important NCERT Questions
Surface Areas and Volumes
NCERT Books for Session 2022-2023
CBSE Board, UP Board and Other state Boards
EXERCISE 13.2
Page No:217
Questions No: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?
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Radius of each pehholder r = 3 cm and height h = 10.5 cm
The penholder is open at the top, therefore, the area of cardboard for 1 penholder = 2πrh + πr²
= 2 × π × 3 × 10.5 + π × 3² = 63π + 9π = 72π cm²
So, the area of cardboard for 35 penholders = 35 × 72π cm²
= 35 × 72 × 22/7 = 5 × 72 × 22 = 7920 cm²
So, Vidhyalaya has to purchase 7920 cm² cardboard for the competition.