Chapter 11: Direct and Inverse Proportions

Math • Class 8

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Chapter Analysis

Intermediate18 pages • English

Quick Summary

This chapter covers the concepts of direct and inverse proportions. Direct proportion occurs when two quantities increase or decrease together at the same rate, whereas inverse proportion happens when one quantity increases while the other decreases. Several real-life examples, such as speed and travel time or number of workers and time taken, illustrate these principles. Exercises are included to enhance understanding through practical application.

Key Topics

  • Direct Proportion
  • Inverse Proportion
  • Real-life Applications
  • Problem-solving using Proportion
  • Exercises on Proportion

Learning Objectives

  • Understand and identify direct and inverse proportions.
  • Apply the concepts of proportion to solve real-life problems.
  • Analyze the relation between varying quantities.
  • Develop problem-solving skills with proportion equations.

Questions in Chapter

A machine in a soft drink factory fills 840 bottles in six hours. How many bottles will it fill in five hours?

Page 137

A photograph of a bacteria enlarged 50,000 times attains a length of 5 cm. What is the actual length of the bacteria?

Page 137

A train is moving at a uniform speed of 75 km/hour. How far will it travel in 20 minutes?

Page 135

Additional Practice Questions

If 20 liters of paint covers an area of 200 square meters, how much paint is needed to cover 500 square meters?

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Answer: Since the paint and area covered are directly proportional, you would need 50 liters of paint to cover 500 square meters.

A car travels a distance in 3 hours at a speed of 60 km/h. What will be the speed if it needs to travel the same distance in 2 hours?

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Answer: Using the inverse proportion of speed and time, the speed needed is 90 km/h.

If the current of a river doubles, the time taken by a boat to cross it will be halved. Explain this using inverse proportion.

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Answer: As the current increases, the time to cross reduces inversely as both are inversely proportional.

Direct and Inverse Proportions - Math Class 8 NCERT PDF | I❤️NCERT