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 `(f_i)`	Class mark `(x_i)`	`f_i x_i`
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	`Ʃf_i = 30`		`Ʃf_i x_i = 2277`

The mean of the data is given by,

x =`(Ʃ_i f_i  x_ i )/(Ʃ_i f_i)`

=`2277/30`

=75.9

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