In which case is it necessary to use an addition table or a number line? Why is it inconvenient?

Solution:

It is necessary to use an addition table or a number line when dealing with problems that are difficult to solve mentally, especially when numbers are large, or when the operation is complex and requires visualization or a systematic approach.

Reasons for inconvenience:

• Number line: It can be inconvenient for large numbers as it would require a very long line, making it impractical to draw or use. It's best for visualizing sums and differences within a smaller range.
• Addition table: While systematic, it can be time-consuming to locate the specific sum among many entries, especially if the numbers are large. It's most useful for basic addition facts and reinforcing number bonds up to 10 or 20.
• Mental calculation: For simple sums (like 6+3), using a table or line is inconvenient because it's slower than doing it mentally.

Conclusion: For complex calculations or when exact visualization is needed, these tools are helpful. For simple, well-known sums, they become inconvenient due to the extra steps involved.