Example 1 · level 1
A train covers 360 km in 8 hours. At the same speed, how far does it go in 15 hours (in km)?
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- For 1: 360 ÷ 8 = 45.
- For 15: 45 × 15 = 675.
Answer: 675
CLASS 8 MATHS · DIRECT AND INVERSE PROPORTIONS
Direct and inverse proportion
Direct: both grow together, so x/y stays the same. Inverse: one grows as the other shrinks, so x × y stays the same.
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Worked examples
Example 2 · level 2
A bus going at 70 km/h takes 13 hours from Ranchi to Patna. How many hours would it take at 130 km/h?
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- Product = 70 × 13 = 910.
- New hours = 910 ÷ 130 = 7.
Answer: 7 hours
Example 3 · level 3
A hostel has food for 80 students for 9 days. How many days will the same food last for 90 students?
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- Product = 80 × 9 = 720.
- New days = 720 ÷ 90 = 8.
Answer: 8 days