Question

Thirty women were examined in a hospital by a doctor and their of heart beats per minute were recorded and summarised as shown. Find the mean heart beats per minute for these women, choosing a suitable method.
Number of heart beats/minute 65-68 68-71 71-74 74-77 77-80 80-83 83-86
Number of women 2 4 3 8 7 4 2

Answer 1

Given:

Thirty women were examined in a hospital by a doctor and their of heart beats per minute were recorded and summarised as shown.  

Number of heart beats/minute 65-68 68-71 71-74 74-77 77-80 80-83 83-86

Number of women 2 4 3 8 7 4 2

To find:

Find the mean heart beats per minute for these women, choosing a suitable method.

Solution:

From given, we have,

Number of heart beats/minute 65-68 68-71 71-74 74-77 77-80 80-83 83-86

Number of women 2 4 3 8 7 4 2

Consider the attached figure for referring a frequency table.

From the figure it's clear that,

∑ fi = 30

∑ fi × xi = 12

Let the average mean = a = 75.5

So, we have,

Mean = a + ∑ (fi × xi)/∑ fi

= 75.5 + 12/30

= 75.5 + 0.4

= 75.9

Therefore, the mean heart beats per minute for these women is 75.9