NCERT Class 9 Solutions: Surface Areas and Volumes (Chapter 13) Exercise 13.1 – Part 1
Q1 A plastic box long, wide and deep is to be made. It is opened at the top. Ignoring the thickness of the plastic sheet, determine:

The area of the sheet required for making the box.

The cost of sheet, if a sheet measuring costs .
Solution:

Plastic box length is

Plastic box width is

Plastic box depths is
Solution (i) The area of sheet required to make the box is equal to the surface area of the box excluding the top.
The sheet required required to make the box is
Solution (ii) Cost of of sheet
∴ Cost of of sheet
Q2 The length, breadth and height of a room are respectively. Find the cost of white washing the walls of the room and the ceiling at the rate of
Solution:

The room length is

The room breadth is

The room height is
Area of four walls including the ceiling = Area of walls ( + area of ceiling ()
Cost of white washing
Total cost
Q3 The floor of a rectangular hall has a perimeter . If the cost of painting the four walls at the rate of is, find the height of the hall.
Solution:

Perimeter of rectangular hall

Total cost of painting

Rate per
Area of four walls =

Now is the perimeter of the floor which is 250 m. Therefore, area of four walls is

Total cost of painting= Area of four walls hall × rate per square m

Therefore, or
So, the height of the hall is