Interpreting -10 as total time saved after Ming's 4 training runs (middle school math)

Here's a step-by-step interpretation of the situation.

1. What does -2.5 minutes per run mean? Each training run is faster by 2.5 minutes compared with the previous time or the starting time.
2. How do we get -10? Multiply the change per run by the number of runs: 4 × (-2.5) = -10.
3. What does -10 tell us? It tells us the total change in Ming's time after those 4 runs is a decrease of 10 minutes compared with the starting time.
4. Write it as a final time If the first time was T minutes, after 4 runs she is at T − 10 minutes. For example, if T = 40, then the final time is 30 minutes.
5. Key idea A negative total change means a reduction in time; the magnitude (10 minutes) is the total amount saved.