Maths Notes for Chapter 11 Direct and Inverse Proportions Class 8 - FREE PDF Download
FAQs on Direct and Inverse Proportions Class 8 Maths Chapter 11 CBSE Notes - 2025-26
1. What key concepts are summarised in the Class 8 Maths Revision Notes for Chapter 11, Direct and Inverse Proportions?
These revision notes provide a concise summary of the core concepts for Chapter 11. They cover the fundamental definitions of direct proportion and inverse proportion, how to identify the relationship between two quantities, and the use of the constant of proportionality (k). The notes also include key formulas and methods for solving word problems related to this chapter.
2. How can I quickly determine if a problem involves direct or inverse proportion during a revision?
A simple way to check is to see how the quantities relate. Ask yourself: if one quantity increases, does the other also increase? If yes, it is direct proportion (e.g., more articles purchased, higher the cost). If one quantity increases while the other decreases, it is inverse proportion (e.g., more workers on a job, less time taken to complete it).
3. What is the main formula to remember for a quick revision of direct proportion?
For a quick revision of direct proportion, the most important formula to remember is that the ratio of the two quantities (x and y) is always constant (k). This is expressed as:
- x/y = k or, more practically for solving problems, x₁/y₁ = x₂/y₂.
4. What is the core principle for solving problems on inverse proportion mentioned in these notes?
The core principle for inverse proportion is that the product of the two quantities (x and y) remains constant (k). The formula to remember for revision is:
- x * y = k or, for problem-solving, x₁ * y₁ = x₂ * y₂.
5. Why is the product of two quantities constant in inverse proportion, while their ratio is constant in direct proportion?
This is because of their fundamental relationship. In direct proportion, two quantities increase or decrease at the same rate, so their ratio (like speed, which is distance/time) remains the same. In inverse proportion, one quantity's increase causes a corresponding decrease in the other to keep a final outcome fixed (like total work done), so their product (e.g., speed × time = fixed distance) remains constant.
6. What is a common mistake to avoid when applying the concepts from these revision notes?
A very common mistake is confusing the formulas. Students often use the direct proportion formula (x₁/y₁ = x₂/y₂) for an inverse proportion problem. During revision, it's crucial to first identify the type of proportion correctly and then apply the appropriate formula: ratio for direct (x/y) and product for inverse (x*y).
7. How do these Class 8 Maths notes help in structuring a quick revision of Chapter 11?
These notes are structured to facilitate a quick and effective revision. They start with the basic definitions, move to the identifying characteristics of each proportion, provide the essential formulas, and conclude with solved examples. This logical flow allows students to recap the entire chapter systematically, reinforcing their understanding for the CBSE 2025-26 exams without needing to read the whole textbook again.
8. What are some real-life examples that help to memorise the difference between direct and inverse proportions?
Thinking of real-life examples is an excellent revision technique.
- For Direct Proportion: The more money you save per month, the more you save in a year (both increase).
- For Inverse Proportion: The higher the speed of a car, the less time it takes to cover a fixed distance (one increases, the other decreases).

















