Question

Suppose a person deposits Rs.$10,000$ in a bank for a simple interest at the rate of $7$% per annum. Obtain a relation for accrued interest in terms of years. Draw the graph of this relation. Use this to read the interest at the end of $10$ years.

Answer 1

Let $y$ be the interest obtained in $x$ years. The interest for $x$ years is $\frac{7}{100}\times 10000\times x=700x$. Thus you get $y=700x$ as the required relation. Now use the scaling; $1$ unit$=700$ along $y$-axis. Note that
for $x=1$, you get $y=700$: $(x,y)=(1,700)$ .
for $x=2$, you get $y=1400$: $(x,y)=(2,1400)$
Take a sheet of graph paper and set up coordinate axes $X^{\prime }OX\leftrightarrow Y^{\prime }OY$
Locate points $P(1,700)$ and $Q(2,1400)$.

Remember you are using the scale $1$ unit $=700$ along $y$-axis. Now the equation is a straight-line and hence $P,Q$ determine this straight-line.