Mean value of time $t_{mean} = \frac{1.25 + 1.24 + 1.27 + 1.21 + 1.28}{5} = \frac{6.25}{5} = 1.25 \text{ s}$. Absolute errors in the measurements are: $\Delta t_1 = |1.25 - 1.25| = 0.00 \text{ s}$ $\Delta t_2 = |1.25 - 1.24| = 0.01 \text{ s}$ $\Delta t_3 = |1.25 - 1.27| = 0.02 \text{ s}$ $\Delta t_4 = |1.25 - 1.21| = 0.04 \text{ s}$ $\Delta t_5 = |1.25 - 1.28| = 0.03 \text{ s}$ Mean absolute error $\Delta t_{mean} = \frac{0.00 + 0.01 + 0.02 + 0.04 + 0.03}{5} = \frac{0.10}{5} = 0.02 \text{ s}$. Percentage relative error $= \frac{\Delta t_{mean}}{t_{mean}} \times 100\% = \frac{0.02}{1.25} \times 100\% = 1.6\%$.