Final answer:
To test the hypothesis that the mean difference between sitting still and jumping times is zero, the times of each activity must be recorded and compared. A statistical test, like a paired t-test, is then used to determine if the difference in means is significant. The number of seconds each activity should be held is not needed for this analysis.
Step-by-step explanation:
The student's question appears to focus on testing a hypothesis regarding the mean difference in seconds between two different activities: sitting still in a relaxed position and jumping. To test their hypothesis that the mean difference would be zero, each of the eight girls' times for both activities should be recorded. Once the times are recorded, the differences for each girl would be calculated, followed by finding the mean (average) difference of those values. If the mean difference is not significantly different from zero using statistical tests, then the girls' hypothesis could not be rejected.
To proceed, they need to use a statistical test, such as a paired t-test, to analyze the data and determine if there is a statistically significant difference between the two mean times. If the p-value is greater than the chosen level of significance (usually 0.05), then the hypothesis that there is no difference is not rejected. This process does not actually require knowing how many seconds the activities should be held; rather, it focuses on comparing the durations of two different tasks.