Question

A bank gives 10% Simple Interest (S.I.) on deposits by senior citizens. Draw a graph to illustrate the relation between the sum deposited and the simple interest earned. Find from your graph

(a) the annual interest obtainable for an investment of ₹ 250.

(b) the investment one has to make to get an annual simple interest of ₹ 70.

Answer 1

Sum deposited	Simple interest for a year
₹ 100	₹ `(100 xx 1 xx 10)/100` = ₹ 10
₹ 200	₹ `(200 xx 1 xx 10)/100` = ₹ 20
₹ 300	₹ `(300 xx 1 xx 10)/100` = ₹ 30
₹ 500	₹ `(500 xx 1 xx 10)/100` = ₹ 50
₹ 1000	₹ 100

We get a table of values.

Deposit (in ₹)	100	200	300	500	1000
Annual S.I. (in ₹)	10	20	30	50	100

(i) Scale : 1 unit = ₹ 100 on horizontal axis; 1 unit = ₹ 10 on vertical axis.

(ii) Mark Deposits along the horizontal axis.

(iii) Mark Simple Interest along the vertical axis.

(iv) Plot the points : (100,10), (200, 20), (300, 30), (500,50) etc.

(v) Join the points. We get a graph that is a line.

1. Corresponding to ₹ 250 on the horizontal axis, we get the interest to be ₹ 25 on the vertical axis.
2. Corresponding to ₹ 70 on the vertical axis, we get the sum to be ₹ 700 on the horizontal axis.