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A school van service in Jaipur lost 20% of its riders this year and now carries 240 students. How many riders did it lose?

Class 8Comparing QuantitiesComparing Quantities
  • A48
  • B60
  • C300
  • D192

Step-by-Step Solution

The 20% is measured on LAST year, so 240 = 0.80 × (last year) → last year = . Riders lost = 300 − 240 = 60. Trap: taking 20% of 240 uses the wrong base and gives 48; 300 is the number carried last year, not the loss.
Answer: B) 60

Key idea: Compound interest — interest on interest

After year 1, interest is added to principal — so year 2's interest is calculated on a LARGER amount, not the original.

****, where A is the final amount after years.
**CI = ** (the total interest earned).

Example: ₹2000 at 5% for 3 years, compounded annually:
- Year 1: Year 2: Year 3:

Direct formula: . CI = 2315.25 − 2000 = 315.25 (vs SI of 300 — compound gives more).

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