A hint to get started
Estimate population mean and variance from a frequency table
The diameters, in mm, of 80 rods selected at random from a large consignment are summarised below.
| Diameter (nearest mm) | 11 | 12 | 13 | 14 | 15 |
|---|---|---|---|---|---|
| Number of rods | 3 | 22 | 31 | 20 | 4 |
Find unbiased estimates of the population mean and variance of the rod diameters.
CJC · Discussion · Question 1
Use the frequencies, so the sample size is 80 rather than the number of table columns.