Question

The rate of interest and the period are given in the table below. Find the interest on Rs 100.

Examples	1	2	3	4	5	6
Rate of interest (p.c.p.a)	8	12	5	9	7	4
Period (years)	5	3	20	4	2	7

Answer 1

We know:
$\mathrm{Interest}=\frac{\mathrm{Principal}\times \mathrm{Rate}\mathrm{of}\mathrm{interest}\left(\mathrm{p}.\mathrm{c}.\mathrm{p}.\mathrm{a}.\right)\times \mathrm{Time}\left(\mathrm{in}\mathrm{years}\right)}{100}$

Given: Principal = Rs 100
The solutions of the subparts are as follows:

(1) Rate of interest = 8 p.c.p.a.
Period = 5 years
Using the above formula, we get:
Interest$=\frac{100\times 8\times 5}{100}$
$$\begin{gathered} =\frac{4000}{100} \\ =40 \end{gathered}$$

Thus, the interest is Rs 40.

(2) Rate of interest = 12 p.c.p.a.
Period = 3 years
Using the above formula, we get:
Interest$=\frac{100\times 12\times 3}{100}$
$$\begin{gathered} =\frac{3600}{100} \\ =36 \end{gathered}$$

Thus, the interest is Rs 36.

(3) Rate of interest = 5 p.c.p.a.
Period = 20 years
Using the above formula, we get:
Interest$=\frac{100\times 5\times 20}{100}$
$$\begin{gathered} =\frac{10000}{100} \\ =100 \end{gathered}$$

Thus, the interest is Rs 100.

(4) Rate of interest = 9 p.c.p.a.
Period = 4 years
Using the above formula, we get:
Interest $=\frac{100\times 9\times 4}{100}$
$$\begin{gathered} =\frac{3600}{100} \\ =36 \end{gathered}$$

Thus, the interest is Rs 36.

(5) Rate of interest = 7 p.c.p.a.
Period = 2 years
Using the above formula, we get:
Interest$=\frac{100\times 7\times 2}{100}$
$$\begin{gathered} =\frac{1400}{100} \\ =14 \end{gathered}$$

Thus, the interest is Rs 14.

(6) Rate of interest = 4 p.c.p.a.
Period = 7 years
Using the above formula, we get:
Interest$=\frac{100\times 4\times 7}{100}$
$$\begin{gathered} =\frac{2800}{100} \\ =28 \end{gathered}$$

Thus, the interest is Rs 28.