Question

During a medical check-up, the number of heartbeats per minute of 30 patients were recorded and summarised as follows:
$\begin{array}{cccccccc}\text{Number of heart-}& & & & & & & \\ \text{beats per minute.}& 65-68& 68-71& 71-74& 74-77& 77-80& 80-83& 83-86\\ \text{Number of patients}& 2& 4& 3& 8& 7& 4& 2\end{array}$ 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	∑fi=30		∑(fi×xi)=2277

The mean of given data is given by

$\overline{x}$ = ∑(fi×xi)/∑fi

= 2277/30

= 75.9

Thus, the mean heartbeats per minute for these patients are 75.9.