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Example 9: (Length and Perimeter)

Draw the graph for the given table. Also write the suitable scales on the axes. Identify independent
and dependent variable.
Side of square ‘a’ (in cm) 2 3 3.5 5 6

Perimeter ‘P’ (in cm) 8 12 14 20 24
Solution:

Perimeter ‘P’ (in cm)

Side of square ‘a’ (in cm)

This is a Linear Graph.
Perimeter of a square = 4 × side
fi P = 4a
Here ‘a’ is an independent variable (can take any value) and ‘P’ is dependent variable (as its value
depends on the value of ‘a’ taken).

Example 10: (Principal and Simple Interest)
A bank gives 10% simple interest (S.I.) on deposits by senior citizens. Draw a graph illustrating
the relation between the sum deposited and simple interest earned. Find from the graph drawn

(a) the annual interest obtainable for an investment of `2500.
(b) the investment one has to make to get an annual simple interest of `600.
Solution: Let the sums deposited by a senior citizen are `1000, `2000, `3000, `5000 and `7000, then
the simple interest earned can be calculated as given below:

Sum deposited (in `) S.I. for one year (in `)
1000 110
××
1000 100 = 100
2000 110
××
2000 = 200
100 Remember
××
3000 110
3000 100 = 300 S.I. = P × R × T
××
5000 110 100
5000 100 = 500 where, P = Principal
7000 110 R = Rate of interest
××
7000 100 = 700 T = Time period

323 Introduction to Graphs