SI = (2/5)P. Using R = (SI×100)/(P×T) = ((2P/5)×100)/(P×10) = (200/5)/10 = 40/10 = 4%. When SI is given as fraction of P, substitute directly and simplify.
FAQ
Common questions and clear answers for this topic.
Simple Interest (SI) is interest calculated only on the original principal amount. Formula: SI = (P x R x T) / 100, where P = Principal, R = Rate of interest per annum, T = Time in years. Amount = P + SI = P(1 + RT/100). Simple Interest is a key topic in SSC CGL, IBPS Bank PO, SBI Clerk, Railway, and all competitive exams.
From SI formula: P = (SI x 100) / (R x T). R = (SI x 100) / (P x T). T = (SI x 100) / (P x R). Example: If SI is Rs 600, Principal Rs 5000, Time 3 years, then Rate = (600 x 100)/(5000 x 3) = 4% per annum. Shortcut: If SI doubles the principal (SI = P), then Time x Rate = 100.
Simple Interest (SI): Interest calculated only on principal. Amount after n years = P + PRT/100. Compound Interest (CI): Interest calculated on principal plus accumulated interest. Amount = P(1 + R/100)^n. CI is always greater than SI for same P, R, T. Difference for 2 years: CI - SI = P(R/100) squared. These formulas help solve comparison problems in banking exams.
Common SI problem types: 1) Find SI when P, R, T given, 2) Find P or R or T when other values given, 3) Money doubles/triples problems, 4) Two investments at different rates. Useful shortcuts: Money doubles when RT = 100. Money becomes 3 times when RT = 200. Money becomes n times when RT = 100(n-1). Practice at least 10 SI problems daily for competitive exam preparation.
Mixed SI problems: If total interest from two loans (P1 at R1% and P2 at R2%) for T years is I, then P1 x R1 + P2 x R2 = I x 100/T. For equal SI from two investments: P1/P2 = R2 x T2 / (R1 x T1). Annual repayment installment formula for equal installments over n years at r% SI also appears in IBPS PO Mains.
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