Skip to main content
Naman Academy For Class 9
Chapter 10: How Quantities Combine: Understanding DataAll 1 Questions on This Page

Class 9 Maths Chapter 10 Exercise Set 10.2 Solutions

Step-by-step solutions for Class 9 Mathematics Ganita Manjari Part 1I Chapter 10 Exercise Set 10.2 (Question 1). Covers weighted mean with ratio weights and combining percentage scores with different maximum marks.

💡 Quick navigation: Tap any question number in the bar below to jump straight to that question and its step-by-step solution.← Chapter Overview
Jump:

Key Concepts for Exercise Set 10.2

Jump to Question 1
1

Weighted Mean with Ratio Weights

When weights are specified in a ratio w₁ : w₂ : w₃, the overall weighted average is obtained by multiplying each value by its corresponding weight and dividing by the sum of the weights.

Weighted Mean = (w₁x₁ + w₂x₂ + w₃x₃) / (w₁ + w₂ + w₃)
2

Normalising Scores with Different Maximum Marks

Raw scores cannot be combined directly when tests have different maximum marks. Each component must first be converted into a common scale (fraction or percentage) before weighting.

Percentage Score = (Marks obtained / Maximum marks) × 100

Savitri’s marks in Kashmiri are as follows: 35 out of 50 in internal tests, 44 out of 60 in the project, and 80 out of 100 in the final exam. The annual percentage score is calculated by combining the internals, project, and final exam in the ratio 3:4:5. Which of the following expression(s) gives her annual score (as a percentage) in Kashmiri?

  • (i)(35 × 3 + 44 × 4 + 80 × 5) / (3 + 4 + 5)
  • (ii)[(35/100) × 3 + (44/100) × 4 + (80/100) × 5] / (3 + 4 + 5)
  • (iii)([(35/50) × 3 + (44/60) × 4 + (80/100) × 5] / (3 + 4 + 5)) × 100
  • (iv)[((35/50) × 100) × 3 + ((44/60) × 100) × 4 + ((80/100) × 100) × 5] / (3 + 4 + 5)
Solution
Given:
Internal tests = 35 out of 50
Project = 44 out of 60
Final exam = 80 out of 100
Ratio of weights = 3 : 4 : 5
Formula:
Weighted Mean = w₁x₁ + w₂x₂ + w₃x₃w₁ + w₂ + w₃

The percentage score for each assessment is:

Internals = 3550 × 100 = 70%
Project = 4460 × 100 = 2203%
Final exam = 80100 × 100 = 80%

Using the weighted mean formula:

Annual score (%) = [70 × 3 + 2203 × 4 + 80 × 5] / (3 + 4 + 5)
= [210 + 8803 + 400] / 12
= 2710312
= 271036
≈ 75.28%

Expression (i) is incorrect because it uses raw marks without considering the different maximum marks.

Expression (ii) is incorrect because it divides all marks by 100, instead of their respective maximum marks.

Expression (iii) is correct because it combines the fractional scores using the given weights and multiplies the result by 100.

Expression (iv) is correct because it converts each score into a percentage before combining the percentages using the given weights.

Answer:Correct expressions: (iii) and (iv) | Annual score (%) ≈ 75.28%

Need to practice other sections in Chapter 10?

Return to Chapter 10 (How Quantities Combine: Understanding Data)→