Question

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

Number of heart beats per minute:	65-58	68-71	71-74	74-77	77-80	80-83	83-86
Number of women:	2	4	3	8	7	4	2

Answer 1

Let the assumed mean be A = 75.5 and h = 3.

No. of Heart Beats per Min:	Mid Value $\left(x_i\right)$	No. of Women $\left(f_i\right)$:	$d_i=x_i-A$	$u_i=\frac{1}{h}\times d_i$	$f_i{u}_i$
65-68	66.5	2	$-$9	$-$3	$-$6
68-71	69.5	4	$-$6	$-$2	$-$8
71-74	72.5	3	$-$3	$-$1	$-$3
74-77	75.5 = A	8	0	0	0
77-80	78.5	7	3	1	7
80-83	81.5	4	6	2	8
83-86	84.5	2	9	3	6
		$\sum f_i=30$			$\sum f_i{u}_i=4$

We know that mean,

Now, we have.

Putting the values in the above formula, we have




Hence, the mean heart beats per minute for women is 75.9.