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:
[tex]\begin{gathered} T_1=\frac{55+68+64+66+70}{5}=\frac{323}{5} \\ T_1=64.6s \\ \\ T_2=\frac{56+58+59+61+57}{5}=\frac{291}{5} \\ T_2=58.2s \end{gathered}[/tex]
Now, calculating the difference, we do as follows:
[tex]\Delta T=T_1-T_2=64.6-58.2=6.4\cong6[/tex]
From the presented solution, and assuming the problem requires the difference of the average time, the answer is C-6
