# Important Questions for Class 9 Chapter 13 - Surface Areas and Volumes

We have come up with the Important Questions for Class 9th which is very benifit for your Final exams. The PDF we provided is absolutly free. Download and Start practicing.

**Important questions based on NCERT syllabus for Chapter 13 - Surface Areas and Volumes:**

*Question 1*: A cylindrical saline bottle has a radius of 7 cm and height of 20 cm. If the saline is released at a rate of 10 cubic cm per second, in approximately how many minutes does the saline bottle get emptied?

*Solution*:

r = 7,h = 20

Volume of the saline bottle = πr^2h

= 22/7 × 72 × 20

= 3080cm^3

No. of seconds needed = 3080/10 = 308s

308 s = 5.13 min

*Question 2*: Raghu had to make a cylindrical tube with an aluminium cover. What is the area of the aluminium sheet he needs to cover the tube if the tube has a length of 1m and base radius 3.5cm? (Take π = 22/7)

*Solution*:

r = 3.5cm,h = 1m = 100cm

Area of Aluminium sheet required = curved surface area of the tube

= 2πrh

= 2 × 22/7 × 3.5 × 100

= 2200cm^2

*Question 3*: 14. A hemispherical bowl made of brass has inner radius of 3.5 cm. Find the cost of tin-plating the inner part of the bowl as well as tin plating a plate that exactly fits as a lid on bowl. Tin plating is done at the rate of Rs.10 per 100 sq.cm.

*Solution*:

Surface area that has to be plated = Curved surface area of the hemisphere bowl + surface area of the plate

= 2πr^2 + πr^2

= 2 × 22/7 × 3.52 + 22/7 × 3.52

= 3 × 22/7 × 3.52

= 115.5cm^2

Hence cost of tin plating = 115.5 × 10/100

= Rs.11.55