Surface Areas & Volumes | Exercise 13.1 | Q1

Question 1: A plastic box 1.5 m long, 1.25 m wide and 65 cm deep is to be made. It is open at the top. Ignoring the thickness of the plastic sheet, determine:
(i) The area of the sheet required for making the box.
(ii) The cost of sheet for it, if a sheet measuring 1 m² costs Rs 20.

Explanatory Answer | Exercise 13.1 Question 1

Dimensions of the Plastic Box

Note that two while the length and width are in metres, height or depth of the box is given in centimetres. Let us convert the height into metres.
Length of the box = 1.5 m
Width of the box = 1.25 m

Height of the box = 65 cm = \\frac{65}{100})m

Part (i): Area of sheet required to make the box

The box is open at the top.
∴ Area of sheet required = Lateral surface area of the cuboid + area of the base

Lateral surface area of cuboid = 2h (l + b)
= 2 × \\frac{65}{100})(1.5 + 1.25) = \\frac{130}{100})(2.75)
= 3.575 m²

Area of the base of cuboid = l x b
= 1.5 × 1.25 = 1.875 m²

Total area of sheet required to make the open box
= 3.575 + 1.875
= 5.45 m²

Part (ii): Cost of the sheet required

Cost of sheet : Rs.20 per m²
Cost of sheet required for the box = Total area of sheet required to make the cuboid box × cost per m²
= 5.45 × 20
= Rs.109

Exercise 13.1 | Surface Area of Cubes & Cuboids

1. Class 9 Exercise 13.1 Question 3 | Height of hall ▶
2. Class 9 Exercise 13.1 Question 6 | TSA of Herbarium ▶
3. Class 9 Exercise 13.1 Question 7 | Shanti Sweets ▶

Exercise 13.2 | Surface Area of Cylinders

1. Class 9 Exercise 13.2 Question 3 | CSA TSA of Metal Pipe ▶
2. Class 9 Exercise 13.2 Question 4 | Roller & Playground ▶
3. Class 9 Exercise 13.2 Question 9 | Cylindrical Petrol Tank ▶
4. Class 9 Exercise 13.2 Question 10 | CSA of Decorative Lampshade ▶

Exercise 13.3 | Surface Area of Cones

1. Class 9 Exercise 13.3 Question 5 | Length of Tarpaulin 3 m wide ▶
2. Class 9 Exercise 13.3 Question 8 | Cost of painting conical barricades ▶

Exercise 13.4 | Surface Area of Spheres & Hemispheres

1. Class 9 Exercise 13.4 Question 8 | Outer CSA of hemispherical bowl ▶
2. Class 9 Exercise 13.4 Question 9 | Surface area of sphere & Cylinder ▶