CBSE Class 8 Maths Revision Notes Chapter 13 – Direct and Inverse Proportions -CoolGyan

Revision Notes for CBSE Class 8 Maths Chapter 13 – Free PDF Download

Free PDF download of Class 8 Maths Chapter 13 – Direct and Inverse Proportions Revision Notes & Short Key-notes prepared by expert Maths teachers from latest edition of CBSE(NCERT) books. All Chapter 13 – Direct and Inverse Proportions Revision Notes to help you to revise complete Syllabus and Score More marks.
Maths NCERT Solutions for Class 8

Chapter Name	Direct and Inverse Proportions
Chapter	Chapter 13
Class	Class 8
Subject	Maths Revision Notes
Board	CBSE
TEXTBOOK	CBSE NCERT
Category	Revision Notes

Quick Revision Notes

Variations: If the values of two quantities depend on each other in such a way that a change in one causes corresponding change in the other, then the two quantities are said to be in variation.
Direct Variation or Direct Proportion:
Two quantities x and y are said to be in direct proportion if they increase (decrease) together in such a manner that the ratio of their corresponding values remains constant. That is if $\frac{x}{y}$ =k [k is a positive number, then x and y are said to vary directly. In such a case if y₁, y₂ are the values of y corresponding to the values x₁, x of x respectively then $\frac{x_{1}}{y_{1}}$ = $\frac{x_{2}}{y_{2}}$ .
If the number of articles purchased increases, the total cost also increases.
More than money deposited in a bank, more is the interest earned.
Quantities increasing or decreasing together need not always be in direct proportion, same in the case of inverse proportion.
When two quantities x and y are in direct proportion (or vary directly), they are written as $x \propto y$ . Symbol $\propto$ stands for ‘is proportion to’.
Inverse Proportion: Two quantities x and y are said to be in inverse proportion if an increase in x causes a proportional decrease in y (and vice-versa) in such a manner that the product of their corresponding values remains constant. That is, if xy = k, then x and y are said to vary inversely. In this case if y₁, y₂ are the values of y corresponding to the values x₁, x₂of x respectively then x₁, Y_{1 =}x₂, y_{2 or} $\frac{x_{1}}{y_{1}}$ = $\frac{x_{2}}{y_{2}}$
When two quantities x and y are in inverse proportion (or vary inversely), they are written as x $x \propto \frac{1}{y}$ . Example: If the number of workers increases, time taken to finish the job decreases. Or If the speed will increase the time required to cover a given distance will decrease.