Surface Areas & Volumes | Exercise 13.4 | Q5

Question 5: A hemispherical bowl made of brass has inner diameter 10.5 cm. Find the cost of tin-plating it on the inside at the rate of Rs.16 per 100 cm².

Explanatory Answer | Exrecise 13.4 Question 5

Step 1: Compute Curved Surface Area of Bowl

Diameter of the hemispherical bowl, d = 10.5 cm
Radius of the hemispherical bowl, r = \\frac{d}{2}) = \\frac{10.5}{2}) cm
Curved surface area of hemisphere = 2 × π × r²
Take π = \\frac{22}{7})
Curved surface area of the hemispherical bowl = 2 × \\frac{22}{7}) × \\frac{10.5}{2}) × \\frac{10.5}{2})
= 11 × 1.5 × 10.5
= 173.25 cm²

Step 2: Compute the Cost of Tin-plating the Bowl

Cost of tin-plating the hemispherical bowl per 100 cm² = Rs. 16
Cost of tin-plating the hemispherical bowl per cm² = Rs. 0.16
Cost of tin-plating the bowl on inside at the rate of Rs.0.16 per cm²= 173.25 × 0.16
= Rs.27.72

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 ▶