## Aptitude question and answer on Simple interest

 1 In how many years will a sum of money double itself at 4% per annum ? A.    8 years B.    16 years C.    12 years D.    25 years Answer : D.  25 years Explanation: Let  Sum = x  Then  S.I = x $\dot{..}$ Time = ${100 \times S.I \over Sum \times Rate}$              =$\bigg({100 \times x \over x \times 4} \bigg)$years              = 25 years Discuss 2 A person borrowed Rs. 1500 at the rate of 5% per annum S.I. what amount will he pay to clear the debt after 4 years ? A.    Rs. 2000 B.    Rs. 1880 C.    Rs. 1800 D.    Rs. 1600 Answer : C.  Rs. 1800 Explanation: Amount = Rs. $\Bigg( 1500+{1500 \times5 \times4 \over100}\Bigg)$=Rs. 1800 Discuss 3 Rajnish took a loan for 7 years at the rate of 6% p.a. S.I. If the total paid was Rs. 2100, the principal was A.    2% B.    5% C.    8% D.    10% Answer : A.  2% Explanation: Rate=$\Bigg( {100 \times 300 \over5000 \times3} \Bigg)\%=2\%$ Discuss 4 At a certain rate of simple interest, a certain sum doubles itself in 10 years. If will triple itself in  A.    12 years B.    15 years C.    20 years D.    30 years Answer : C.  20 years Explanation: Let     sum  = x. Then   S.I.  = x and time = 10 years $\dot{..}$ Rate = $\Bigg( {100 \times x \over x \times 10} \Bigg) \%=10\%$ Now , Sum = x, S.I.=2x , Rate = 10 % $\dot{..}$ Time = $\Bigg( {100 \times 2x \over x \times 10} \Bigg)$years                 = 20 years Discuss 5 The simple interest on Rs. 18200 from March 9, 2001 to May 21, 2001 at of $7{1 \over 2}$ rate percent will be A.    Rs. 290 B.    Rs. 273 C.    Rs. 288 D.    Rs. 225 Answer : B.   Rs. 273 Explanation: March + April + May = 22+30+21                               = 73 days                               =${73 \over 365}$ year                               = ${1 \over 5}$ year $\dot{..}$              Interest  = Rs. $\Bigg(18200 \times{1 \over5} \times {15 \over 2 \times 100} \Bigg)$                               =Rs. 273 Discuss 6 A certain sum of money lent out at S.I. amounts to Rs. 6900 in 3 years and Rs. 7500 in 5 years. The sum lent is A.    Rs. 4000 B.    Rs. 4500 C.    Rs. 5000 D.    Rs. 6000 Answer : A.  Rs. 4000 Explanation: S.I. for 2 years = Rs (7500-6900)                       = Rs. 600 S.I for 3 years = Rs. $\bigg( {600 \over 2} \times 3 \bigg)$                       =Rs. 900 $\dot{..}$     Principal = Rs. (6900-900)                      = Rs. 6000 Discuss 7 A Sum of money triples itself in 15 years 6 months. in how many years would it double itself ? A.    6 years 3 months B.    7 years 9 months C.    8 years 3 months D.    9 years 6 months Answer : B.   7 years 9 months Explanation: Let sum = x. Then  S.I.=2x and Time = $31 \over 2$years $\dot{..}$ Rate = $\Bigg({100 \times 2x \over x} \times{2 \over31} \Bigg)\%$            =$\bigg({400 \over 31} \bigg)\%$ Now,       Sum=x,    S.I.=x and      Rate = $\bigg({400 \over 31} \bigg)\%$ $\dot{..}$ Time = $\Bigg({100 \times x \over x} \times{31 \over 400} \Bigg)$year             =7 years 9 months. Discuss 8 For how many years should Rs. 1200 be invested at 10% p.a. in order to earn the same simple interest as is earned by investing Rs. 1800 at 12% p.a. for 5 years ? A.    9 B.    10 C.    12 D.    11 Answer : A.  9 Explanation: S.I required = Rs. $\Bigg({1800 \times 12 \times 5 \over 100} \Bigg)$                  = Rs. 1080          Time = $\Bigg({1800 \times 1080 \over 1200 \times10} \Bigg)$years                  = 9 years Discuss