If we assume that the answer wants the difference of time of the average time of the groups 1 and 2, we need to calculate it as follows:
Average time for groups 1 and 2:
![\begin{gathered} T_1=(55+68+64+66+70)/(5)=(323)/(5) \\ T_1=64.6s \\ \\ T_2=(56+58+59+61+57)/(5)=(291)/(5) \\ T_2=58.2s \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/3qjt671vnf2vtbx7cyuvavytcru4l3sthj.png)
Now, calculating the difference, we do as follows:
![\Delta T=T_1-T_2=64.6-58.2=6.4\cong6](https://img.qammunity.org/2023/formulas/mathematics/college/a40lwuffafy54g7u2jk47b75f0vvs844le.png)
From the presented solution, and assuming the problem requires the difference of the average time, the answer is C-6