IBPS PO-RRB QUANT NIGHT REVISION PART-1

Compound Interest

• Assume that two persons together lent Rs. P at R% compound interest in such a way that the amount one person gets after T₁ years is same as the amount other person gets at the end of T₂ years. Then,
  
  Share of the first person in the principal = P1+(100100+R)n    where n = T₂ - T₁


• The difference between compound interest and simple interest on Rs. P for 2 years at R% per annum
  
  =P(R100)2
  
  =R×SI2×100


• The difference between compound interest and simple interest on Rs. P for 3 years at R% per annum
  
  =P(R100)2(R100+3)
  
  =SI3[(R100)2+3(R100)]


• If a sum of money becomes n₁ times in t₁ years at compound interest and n₂ times in t₂ years, then
  
  t2=t1log n2log n1


• If a certain sum becomes n times in t years at compound interest, then the same sum becomes n^m times in mt years


• If a certain sum becomes n times in t years, then the rate of compound interest can be given by
  
  R=[(n)1/t−1]×100%


• If a certain sum of money at compound interest amounts to Rs.x in t₁ years and Rs.y in t₂ years, then the rate of interest per annum can be given by
  
  R=[(yx)1/(t2−t1)−1]×100%


• If a loan of Rs. D at R% compound interest per annum is to be repaid in n equal yearly instalments, then the value of each instalment can be given by
  
  D(100100+R)+(100100+R)2+⋯+(100100+R)n