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Class 8
Chapter 7: Proportional Reasoning
A ratio compares two quantities (like 2:3). A proportion is two equal ratios. In direct proportion, both quantities grow together; in inverse proportion, one grows as the other shrinks.
Learning outcomes
- Use ratios and proportions to compare quantities
- Solve direct and inverse proportion problems
Activities
- Recipe & map-scale proportion tasks
Worked examples
Read through these first, then try the practice below.
Example 1 — Direct proportion
If 4 pens cost ₹60, what do 7 pens cost at the same rate?
Solution: Cost per pen = 60 ÷ 4 = ₹15. So 7 pens cost 7 × 15 = ₹105.
Example 2 — Inverse proportion
If 5 workers take 12 days to finish a job, how long for 10 workers (same speed)?
Solution: Doubling workers halves the time: 12 ÷ 2 = 6 days.
Self-do practice
Question 1 of 3 · Score 0/0If 3 books cost ₹120, what do 5 books cost?
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