Question

During a medical check-up, the number of heartbeats per minute of 30 patients were recorded and summarized as follows:

Number of heartbeats per minute	65−68	68−71	71−74	74−77	77−80	80−83	83−86
Number of patients	2	4	3	8	7	4	2

Find the mean heartbeats per minute for these patients, choosing a suitable method.

Answer 1

Using Direct method, the given data is shown as follows:

Number of heartbeats per minute	Number of patients (fi)	Class mark (xi)	fixi
65−68	2	66.5	133
68−71	4	69.5	278
71−74	3	72.5	217.5
74−77	8	75.5	604
77−80	7	78.5	549.5
80−83	4	81.5	326
83−86	2	84.5	169
Total	$\sum fi=30$		$\sum fixi=2277$

The mean of given data is given by

$\overline{x}=\frac{\sum fixi}{\sum fi}$

$=\frac{2277}{30}=75.9$

​Thus, the mean heartbeats per minute for these patients is $75.9$.