A student uses a Geiger-Muller tube to measure the background radiation count rate over four separate one-minute intervals. The results are shown in the table below.
| 1st count rate | 2nd count rate | 3rd count rate | 4th count rate | |
|---|---|---|---|---|
| count rate in cpm | 43 | 47 | 41 | 45 |
Calculate the mean of the four count rate measurements shown in the table.