Question :
| Number of heart beats 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 |
Solution :
Let assumed mean a = 75.5
| Number of heart beats | No. of women \(f_i\) | Mid Value \(x_i\) | \(d_i\) = \(x_i – a_i\) | \(f_id_i\) |
| 65 – 68 | 2 | 66.5 | -9 | -18 |
| 68 – 71 | 4 | 69.5 | -6 | -24 |
| 71 – 74 | 3 | 72.5 | -3 | -9 |
| 74 – 77 | 8 | 75.5 | 0 | 0 |
| 77 – 80 | 7 | 78.5 | 3 | 21 |
| 80 – 83 | 4 | 81.5 | 6 | 24 |
| 83 – 86 | 2 | 84.5 | 9 | 18 |
| \(\sum f_i\) = 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
