A radiation protection officer uses a portable scintillation counter to monitor the ambient background radiation rate in an analytical chemistry laboratory. The officer records the count rate over four separate ten-second intervals, obtaining the data shown in the table below.
| 1st count rate | 2nd count rate | 3rd count rate | 4th count rate | |
|---|---|---|---|---|
| Count rate (cps) | 26 | 31 | 25 | 30 |
Calculate the mean background count rate, in cps, from these four measurements.