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

Number of heartbeats per 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

From the given data, let us assume the mean as A = 75.5
Class size (h) = 3

So, \(u_i \ = \ \frac{x_i \ - \ A}{h} \ \)
\( \Rightarrow \ u_i \ = \ \frac{x_i \ - \ 75.5}{h} \)

\( \overline{x} \ = \ A \ + h \frac{ \sum \ f_i x_i}{ \sum f_i} \)

\(= 75.5 \ + \ 3 \ × \ \frac{4}{30} \ \)
\( = \ 75.5 \ + \ \frac{4}{10} \ \)
\( = \ 75.9 \)

\(\therefore \) The mean heart beats per minute for these women is 75.9