Surface Areas of Cuboids | Exercise 13.1 | Q2

Question 2: The length, breadth and height of a room are 5 m, 4 m and 3 m respectively. Find the cost of white washing the walls of the room and the ceiling at the rate of Rs.7.50 per m².

Explanatory Answer | Exercise 13.1 Question 2

Given Data: Dimensions of the Room

Length of the room = 5 m
Width of the room = 4 m
Height of the room = 3 m

Step 1: Identify area of surface to be white washed

Area of surface to be white washed = Area covered by walls + Area of ceiling

Step 2: Compute area of surface to be white washed

Area covered by walls = Lateral surface area of the room = 2h (l + b)
= 2 × 3 (5 + 4) = 2 × 3 × 9 = 54 m²

Area of ceiling = l × b
= 5 × 4 = 20 m²

Area of surface to be white washed = Area covered by walls + area of ceiling
= 54 + 20
= 74 m²

Step 3: Cost of white washing

Cost of white washing = Area of white washed surface × Rate per m²
= 74 × 7.5
= Rs.555

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 ▶