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 Keynotes 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 xyxy=k [k is a positive number, then x and y are said to vary directly. In such a case if y_{1}, y_{2} are the values of y corresponding to the values x_{1}, x of x respectively then x1y1x1y1 = x2y2x2y2.  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∝yx∝y. Symbol ∝∝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 viceversa) 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 y_{1}, y_{2} are the values of y corresponding to the values x_{1}, x_{2 }of x respectively then x_{1}, Y_{1 = }x_{2}, y_{2 or }x1y1x1y1 = x2y2x2y2
 When two quantities x and y are in inverse proportion (or vary inversely), they are written as x x∝1yx∝1y. 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.