Finding P or n or r with Multiples

Recap on simple interest Amount = Principal + Interest Where n is in years

Amount = Principal + Interest Example1 : - A certain sum of money amounts to Rs.10,080 in 5 years at 8 %. Find the principal. Solution Given: Amount(A)=10080 , no of years(n)= 5 , rate(r)= 8 To find: Principal(p) We know that 2 20 5 Amount = Principal + Interest 1440 Ans: Principal = Rs 7200 p =1440 x 5 =7200

Example 2 A sum of money doubles itself in 10 years Example 2 A sum of money doubles itself in 10 years. Find the rate of interest Solution Given: Period(n)=10 , A=double of principal=2P, To find: Rate(r) All value is given except value I. So lets find I We Know that I=A-P = 2P-P=P (∵A=2P) Ans: Rate (r) = 10% yearly

Example 3: A sum of money doubles itself at 10 % per annum over a certain time. Find the number of years. Solution Given: Rate(r)=10 , A=double of principal=2P, To find: Rate(r) All value is given except value I. So lets find I We Know that I=A-P = 2P-P=P (∵A=2P) Ans: Period(n) = 10 years

Example 4: A certain sum of money amounts to Rs 5,750 in years and Rs 6,500 in 3 years respectively . Find the principal and the rate percent. Solution Given: Period 1: Amount(A1)=5750, Period (n1) = Period 2: Amount(A2)=6500, Period (n2) = 3 To find: Principal(P), Rate(r) From period 1 to Period 2 Years passed=n2 - n1= Interest earned = A2- A1= 6500-5750 =750 In years Interest earned Rs 750

Ans: Principal(P)=Rs 5000 and Rate (r) = 10% yearly Now lets calculate Interest(S.I2) ,Principal(P) and rate(r) based on period2 Interest earned in Period 2 (S.I2) = Interest per year x 3=500 x 3 =Rs 1500 We know that P = A2 - I2 ∴ P = 6500 - 1500=Rs 5000 Ans: Principal(P)=Rs 5000 and Rate (r) = 10% yearly

Try these 1. A certain sum of money amounts to Rs.10,080 in 5 years at 8 % . Find the principal. 2. Radhika deposited some money and it triples itself at 4% per annum. Find the number of years.