Question

a certain sum of money is invested at the rate of 10% per annum compound interest the interest compounded annually is the difference between the interest of the third year and first year is 1105 find the sum invested

Answer 1

For Annual compound intrest,Amount A at the end of n years is given by 
  A =  where, r is rate of intrest expressed as  percentage 

Rate of intrest on a amount C =c*r where r is rate of intrest expressed as  percentage
Let , the invested amount be P
rate of intrest r=10/100=0.1 

Intrest of first year = P * 10/100 = 0.1P
Amount at the end of second year = A2=
Intrest of third year = A2*0.1

Given , difference between intrest of third year and first year is rs.1105

So, 0.1*P*  - 0.1P = 1105

0.1P() = 1105

0.1P(0.21) = 1105

P = Rs.52619