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A dairy cooperative in Anand collects 25000 litres of milk a day, and the daily collection is growing 20% a year. By how many litres will the daily collection have grown after 3 years?

Class 8Comparing QuantitiesComparing Quantities
  • A18200 litres
  • B15000 litres
  • C11000 litres
  • D43200 litres

Step-by-Step Solution

Growth compounds: litres, so the growth = 43200 − 25000 = 18200 litres. Trap: 15000 litres adds 20% of the ORIGINAL three times (60% of 25000) and so misses the growth on growth; 11000 litres stops after 2 years and 43200 litres is the new total, not the increase.
Answer: A) 18200 litres

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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