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

## 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 xyxy=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 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 xyx∝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 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, xof x respectively then  x1, Y1 = x2, y2 or x1y1x1y1 = x2y2x2y2
• When two quantities x and y are in inverse proportion (or vary inversely), they are written as x x1yx∝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.