To find the day with the greatest change in the number of visitors, we need to look at the absolute values of the changes for each day:

• Monday: +127 → |127| = 127
• Tuesday: -18 → |18| = 18
• Wednesday: +19 → |19| = 19
• Thursday: -209 → |209| = 209

The greatest absolute change occurred on Thursday with a change of 209 visitors.

Would you like more details on how these calculations work? Here are 5 related questions to explore this further:

1. What is the significance of absolute value in real-world problems?
2. How can we represent both positive and negative changes graphically?
3. If we wanted the average change over these four days, how would we calculate it?
4. How would this problem change if we were looking for the smallest change instead?
5. What if there were more days, how would we find the greatest change efficiently?

Tip: When comparing changes, always look at the absolute values to determine the magnitude of change, regardless of direction (increase or decrease).