Compound Interest (Using Formula)
ICSE · Class 9 · Mathematics
Quick revision notes for Compound Interest (Using Formula) — ICSE Class 9 Mathematics. Key concepts, formulas, and definitions for last-minute revision.
Key Topics to Revise
Basic Compound Interest Formula
- When interest is compounded yearly, we use the formula A = P(1 + r/100)ⁿ
- Compound Interest = Amount - Principal = A - P
- Direct formula for CI: CI = P[(1 + r/100)ⁿ - 1]
Different Rates for Successive Years
- When rates differ each year, multiply separate growth factors
- Each year is calculated independently with its own rate
- The formula extends naturally: A = P(1 + r₁/100)(1 + r₂/100)(1 + r₃/100)...
Inverse Problems
- Finding principal when amount is given: P = A/(1 + r/100)ⁿ
- Finding rate when principal and amount are given: solve (1 + r/100)ⁿ = A/P
- Finding time when principal, amount and rate are given: solve for n
Half-Yearly Compounding
- When compounded half-yearly, rate is divided by 2 and time is multiplied by 2
- Formula becomes: A = P(1 + r/(2×100))^(n×2)
- More frequent compounding results in higher returns
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