Simple Interest

Interest calculated only on the original principal — the simpler half of the Interest topic pair.

📖 ~4 min read 📐 RRB NTPC / Group D — Mathematics

SI = (P × R × T) / 100, where P = Principal, R = Rate % per annum, T = Time in years
Amount (A) = P + SI

If a sum becomes "n times" itself in T years at SI: Rate = [(n−1) × 100] / T
SI is the same every year — multiply one year's SI by the number of years directly
Time in months must be converted to years: T = (months)/12

💡 Example: Find SI on ₹12,000 at 8% p.a. for 3 years → SI = (12000×8×3)/100 = ₹2,880

💡 Example: A sum triples in 8 years at SI. Rate = [(3−1)×100]/8 = 25%

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