31. The compound interest on Rs.30000 at 7% per annum for a certain time is Rs.4347. The time is :
a. 2 years
b. $2\displaystyle\frac{1}{2}$ years
c. 3 years
d. 4 years

Answer: C

Explanation:
$30000 \times {\left( {1 + \displaystyle\frac{7}{{100}}} \right)^t} = 30000 + 4347$
or ${\left( {\displaystyle\frac{{107}}{{100}}} \right)^t} = \displaystyle\frac{{34347}}{{30000}} = \displaystyle\frac{{11449}}{{10000}} = {\left( {\displaystyle\frac{{107}}{{100}}} \right)^2}$
Time = 2 years

32. Rs.800 at 5% per annum compound interest will amount to Rs.882 in :
a. 1 year
b. 2 years
c. 3 years
d. 4 years

Answer: B

Explanation:
Let time be t years
$882 = 800{\left( {1 + \displaystyle\frac{5}{{100}}} \right)^t} = \displaystyle\frac{{882}}{{800}} = {\left( {\displaystyle\frac{{21}}{{20}}} \right)^t}$
= ${\left( {\displaystyle\frac{{21}}{{20}}} \right)^2} = {\left( {\displaystyle\frac{{21}}{{20}}} \right)^t} \Rightarrow t = 2$
Time = 2 years

33. Simple interest on a sum at 4% per annum for 2 years is Rs.80.The compound interest on the same sum for the same period is :
a. Rs.81.60
b. Rs.160
c. Rs.1081.60
d. None of these

34. The difference of compound interest on Rs.800 for 1 year at 20% per annum when compounded half-yearly and quarterly is :
a. Nil
b. Rs.2.50
c. Rs.4.40
d. Rs.6.60

35. The difference between simple interest and the compound interest on Rs.600 for 1 year at 10% per annum, reckoned half-yearly is :
a. Nil
b. Rs.6.60
c. Rs.4.40
d. Rs.1.50