Question

If a certain sum at a certain rate of simple interest amount to rs. 3,810 in 3 years and rs. 4,890 in 7 years, then the sum and rate of interest are

Answer 1

Answer:

Sum = rs 3000

Interest rate = 9 % per annum

Step-by-step explanation:

Let say Principle = P

Rate of interest = r % per annum

Interest for 3 years = P * r * 3 / 100 =  3Pr /100

Amount after 3 years = P + 3Pr/100

 P + 3Pr/100  = 3810     - EqA

Interest for 7 yeard = P * r * 7/100 = 7Pr/100

Amount after 7 years = P + 7Pr/100   - EqB

P + 7Pr/100  = 4890   - EqB

EqB - EqA

P + 7Pr/100  - ( P + 3Pr/100 )= 4890 - 3810

4Pr/100 = 1080

Pr/100 = 270

Putting this in eq A

P + 3*270 = 3810

P = 3000

3000*r/100 = 270

30r = 270

r = 9 % per annum