Master Simple Interest from Zero

When you borrow money from a bank, you pay extra money called interest. Simple Interest means the interest is calculated only on the original amount (principal) every year — not on interest earned. Example: You borrow ₹1000 at 10% per year for 3 years. SI = 1000×10×3/100 = ₹300. Total repay = ₹1300.

Key Formulas

Simple Interest

SI = (P × R × T) / 100

P=Principal, R=Rate% per annum, T=Time in years

Principal

P = (SI × 100) / (R × T)

Use when SI, R, T are given.

Rate

R = (SI × 100) / (P × T)

Use when SI, P, T are given.

Time

T = (SI × 100) / (P × R)

Use when SI, P, R are given.

Amount

Amount = P + SI = P(1 + RT/100)

Amount = Principal + Interest

⚡ Shortcut Tricks

If SI = Principal, then RT = 100. Easy to find missing value!

If money doubles in T years at R%, then RT = 100. Example: doubles in 5 years → R = 20%.

If money triples in T years: 2P = SI → 2×100 = RT → RT = 200.

Rate conversion: Monthly rate to yearly → multiply by 12. Daily rate → multiply by 365.

✏️ Solved Examples

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