K borrowed a certain sum at SI. If instead the sum was borrowed at CI, d intrst for d first 2 years increases by Rs 100, while the total intrst for d first 3 years increases by Rs 305. Find d sum

Hi Ravi
Sum for second year will increase in CI because of the interest on the interest for the first year. While the amount in 3rd year increases because of the interest which is earned on the interest of first two years. Interest on first years interest is Rs 100 , and on third years is 105. (That's why for third year 100+100+105 =305)
So rate of interest is 5% per annum.
Since 2nd years interest was 100 rs greater, so Principal must have been 40000.
I have tried to answer it without using equations but if you want the method which makes use of equations, then I can provide that also but I feel this is a better method.