1. **State the problem:** We need to calculate the mean (average) of the given volumes: 25 cm^3, 27 cm^3, 28 cm^3, 21 cm^3, and 25 cm^3. 2. **Add all the volumes:** $$25 + 27 + 28 + 21 + 25 = 126$$ 3. **Count the number of volumes:** There are 5 volumes. 4. **Calculate the mean:** $$\text{Mean} = \frac{\text{Sum of volumes}}{\text{Number of volumes}} = \frac{126}{5} = 25.2$$ 5. **Write the final answer:** The mean volume is **25.2 cm^3**.