Question

theThe difference between si and ci on a sum of money for 2 years is Rs. 15. The si on the same sum for 4 years is Rs. 1200. Find the sum and rate of interest​

Answer 1

Answer:

The other answer given is correct but I will formulate it differently in case that helps some readers

Firstly CI is compound interest

SI is simple intérêts

We are asked to solve for the rate r which in two years has a future value (1 + r )^2 and has we calculated the future value using Simple interest method it be 1% less

Therefore CI - SI = 0.01

So you can solve (1+r)^2 - (1 + 2 r ) = 0.01

Expand to 1+ 2r + r^2 -1 -2r = 0.01

r^2 = 0.01 therefore r = 0.01)^1/2

r = 0.10. Or 10%