Question

Draw a frequency polygon of the following data:

$CI$	$10-19$	$20-29$	$30-39$	$40-49$	$50-59$	$60-69$	$70-79$	$80-90$
$f$	$3$	$7$	$5$	$11$	$6$	$8$	$4$	$5$

Answer 1

We can also draw a frequency polygon without drawing the histogram. We shall understand this.
Observe that the class intervals are given in inclusive form. They are to be converted in to exclusive form by adding the correction factor. The correction factor is $0.5$. This is subtracted from the lower limit and added to the upper limit. Converting the data into exclusive form we get:

CI	$9.5-19.5$	$19.5-29.5$	$29.5-39.5$	$39.5-49.5$	$49.5-59.5$	$59.5-69.5$	$69.5-79.5$	$79.5-89.5$
M.P.	$14.5$	$24.5$	$34.$	$44.5$	$54.5$	$64.5$	$74.5$	$84.5$
$f$	$3$	$7$	$5$	$11$	$6$	$8$	$4$	$5$

Now take a suitable scale for class intervals on X-axis and corresponding frequency on Y-axis. Plot the frequency against the midpoint of the class interval and join these points by line segments to get the frequency polygon.