其它
\textbf{High school students from track teams in the state participated in a training program to improve running times. Before the training, the mean running time for the students to run a mile was 402 seconds with standard deviation 40 seconds. After completing the program, the mean running time for the students to run a mile was 368 seconds with standard deviation 30 seconds. Let X represent the running time of a randomly selected student before training, and let Y represent the running time of the same student after training. Which of the following is true about the distribution of X - Y ?} 
Overseas Competition->Knowledge Point->Calculation Modules
\textbf{Mean: 402 - 368 = 34}  \textbf{SD: X and Y are not independent, correlation is unknown → SD unknown} 