Interest: SI and CI Complete Guide

Simple Interest

• SI = (P × R × T) / 100
• Amount = P + SI
• P = Principal, R = Rate%, T = Time

Compound Interest

• Amount = P(1 + R/100)ⁿ
• CI = Amount - P
• For half-yearly: n = 2t, R = R/2
• For quarterly: n = 4t, R = R/4

Difference between CI and SI

• For 2 years: CI - SI = P(R/100)²
• For 3 years: CI - SI = P(R/100)²(3 + R/100)

Installments

• EMI formula: [P × R × (1+R)ⁿ] / [(1+R)ⁿ - 1]

Population Growth

• Final population = Initial × (1 + Growth%/100)ⁿ
• Depreciation: Final value = Initial × (1 - Depreciation%/100)ⁿ

CAT Tip

• For small rates, CI ≈ SI + (SI × R/200) for 2 years
• Memorize (1.1)² = 1.21, (1.05)² = 1.1025