The task is to round each number to the nearest hundred. Here's the solution for each:

1. 668: The tens digit is 6, which is greater than or equal to 5. Therefore, we round up to 700.
2. 404: The tens digit is 0, which is less than 5. So, we round down to 400.
3. 649: The tens digit is 4, which is less than 5. Hence, we round down to 600.
4. 489: The tens digit is 8, which is greater than or equal to 5. Thus, we round up to 500.

The answers are as follows:

• 668 → 700
• 404 → 400
• 649 → 600
• 489 → 500

Would you like more details or have any questions about rounding?

Here are some related questions you can explore:

1. How do you round numbers to the nearest ten?
2. What is the rule for rounding numbers up or down?
3. How would you round numbers to the nearest thousand?
4. How can rounding help in estimating calculations quickly?
5. What happens when the tens digit is exactly 5?

Tip: When rounding numbers, always focus on the digit in the place you are rounding to (like tens, hundreds, etc.), and use the next smaller digit to decide whether to round up or down.