Thirty women were examined in a hospital by a doctor and the number of heart beats per minute were recorded and summarised as follows. Find the mean heart beats per minute for these women, choosing a suitable method.

Question :

Number of heart beats per minute65 – 6868 – 7171 – 7474 – 7777 – 8080 – 8383 – 86
Number of women2438742

Solution :

Let assumed mean a = 75.5

Number of heart beatsNo. of women \(f_i\)Mid Value \(x_i\)\(d_i\) = \(x_i – a_i\)\(f_id_i\)
65 – 68266.5-9-18
68 – 71469.5-6-24
71 – 74372.5-3-9
74 – 77875.500
77 – 80778.5321
80 – 83481.5624
83 – 86284.5918
\(\sum f_i\) = 30\(\sum f_id_i\) = 12

Mean = a + \(\sum f_id_i\over \sum f_i\) = 75.5 + \(12\over 30\) = 75.5 + 0.4 = 75.9

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