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.
**A=P×(1+R/100)T**, where A is the final amount after T years.
**CI = A−P** (the total interest earned).
Example: ₹2000 at 5% for 3 years, compounded annually:
- Year 1: 2000×1.05=2100− Year 2: 2100×1.05=2205− Year 3: 2205×1.05=2315.25
Direct formula: A=2000×(1.05)3=2315.25. CI = 2315.25 − 2000 = 315.25 (vs SI of 300 — compound gives more).