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: 9 Part:2
Find how much steel was actually used, if 1/12 of the steel actually used was wasted in making the tank.
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Total surface area of cylindrical Petrol storage tank = 2πr(r + h)
= 2 × 22/7 × 2.1 × (2.1 + 4.5) = 2 × 22/7 × 2.1 × 6.6 = 87. 12 m²
Let, the area of steel used to make this cylindrical petrol storage tank = x m²
Steel get wasted in preparation of petrol storage tank = 1/12x m²
Therefore, the total steel used in cylindrical petrol storage tank = x – 1/12x = 11/12x m²
According to the questions: 11/12x = 87.12 ⇒ x = 87.12 × 12/11 = 95.04 m²
Hence, 95.04 m² steel is required to make this cylindrical petrol storage tank.