🎙 Teacher-Style Introduction

Simple Interest (SI) aur Compound Interest (CI) dono DP Constable exam ke scoring topics hain. SI ke questions direct 2–3 steps mein solve ho jaate hain. CI ke questions mostly 1 year or 2 year ke hote hain. Agar formula clear ho, toh calculation 30 seconds se kam mein hoti hai.

📘 Important Formulas / महत्वपूर्ण सूत्र

🔹 Simple Interest (SI)

• SI = (P × R × T) / 100
• Amount = P + SI

🔹 साधारण ब्याज (SI)

• SI = (मूलधन × ब्याज दर × समय) / 100
• राशि = मूलधन + ब्याज

🔹 Compound Interest (CI)

For annually compounded interest:

• Amount = P (1 + R/100)^T
• CI = Amount − P

🔹 चक्रवृद्धि ब्याज (CI)

• राशि = P (1 + R/100)^T
• CI = राशि − मूलधन

⚡ Tricks & Shortcuts / ट्रिक्स व शॉर्टकट

• SI हमेशा linear hota hai — interest har saal same.
• CI mein “interest on interest” hota hai — yearly multiplication method best.
• 2 saal ke CI ka shortcut: CI = SI(2 years) + (SI on SI)
• Rate agar 10% ho toh 1.1 se multiply, 5% ho toh 1.05 se multiply.
• DP exam mein CI zyada tough nahi आता — mostly 1–2 saal ke questions होते हैं.

✔ Solved Examples / हल प्रश्न

Example 1 – SI: P = ₹1000, R = 10%, T = 2 years.
Solution: SI = (1000×10×2)/100 = ₹200, Amount = 1200.

Example 2 – SI: Find SI on ₹1500 at 8% for 3 years.
SI = (1500×8×3)/100 = ₹360.

Example 3 – CI 1 year: P = ₹2000, R = 5%
Amount = 2000×1.05 = ₹2100, CI = 100.

Example 4 – CI 2 years: P = ₹1000, R = 10%
Year 1 = 100, Year 2 = 110 (interest on 1100).
CI = 100 + 110 = 210.

Example 5 – Difference between CI & SI (2 years):
Diff = SI × (R/100) = (P×R×2/100) × (R/100) = P×R²/10000.

Example 6: SI on ₹600 at 12% for 4 years = (600×12×4)/100 = 288.

Example 7: Amount after 2 years at 20% CI on ₹500?
500 → 600 → 720 ⇒ Amount = 720.

Example 8: Find CI for 2 years on ₹4000 at 5%.
Amount = 4000×1.05×1.05 = 4000×1.1025 = ₹4410, CI = 410.

✔ MCQs (Delhi Police Pattern)

1. Find SI on ₹800 at 10% for 2 years. Ans: 160
2. P = 1000, R = 5%, T = 3 years. SI = ? Ans: 150
3. CI on ₹2000 at 10% for 1 year = ? Ans: 200
4. Amount at CI on 500 for 2 years at 20%. Ans: 720
5. Difference between SI & CI for 2 years on ₹1000 at 10%? Ans: 10
6. Find SI for ₹400 at 15% for 2 years. Ans: 120
7. Find CI on ₹1000 at 5% for 2 years. Ans: 102.50
8. SI on ₹600 for 3 years at 8% = ? Ans: 144
9. P = 1200, R = 6%, T = 2 years. SI = ? Ans: 144
10. Find CI for ₹5000 at 10% for 1 year. Ans: 500

💡 Motivation: SI/CI strong hone ka matlab banking + money sense strong — यही real officer ki सोच है. Aage badhiye! 🚓🔥