One hundred test specimens made of grey cast iron FG 300 are tested on a universal testing machine to determine the ultimate tensile strength \left(S_{u t}\right) of the material. The results are tabulated as follows:
Frequency | Class interval (N/mm²) |
2 | 261–280 |
12 | 281–300 |
50 | 301–320 |
32 | 321–340 |
4 | 341–360 |
Calculate: (i) the mean; (ii) the variance; and (iii) the standard deviation for this sample.