Add decimal numbers using efficient written or mental methods

When adding decimal numbers, the most efficient method often depends on the specific numbers involved. For example, with the sum 5.78 + 4.99, the efficient strategy would be to recognise that 4.99 is just one hundredth less than 5, making the sum almost equivalent to adding 5.78 + 5, which is a simpler calculation. Similarly, when adding 5.78 + 4.3, aligning the decimal points and treating 4.3 as 4.30 can simplify the process. The efficiency in these methods comes from simplifying the numbers involved, either by rounding or by aligning decimal points to make the addition process more straightforward.

Continuing with the theme of efficiency, adding numbers like 6.47 + 3.5 can be made easier by viewing 3.5 as 3.50, which aligns the decimal places. In the case of 6.47 + 3.98, recognising that 3.98 is close to 4 allows for a quick mental adjustment. The key to efficiency is to look for patterns or near numbers that simplify the mental calculation. For instance, adding 6.47 to just over 3 results in just over 9, and similarly, adding 6.47 to just under 4 results in just under 10. These strategies reduce the cognitive load, making the addition of decimal numbers faster and more efficient, whether done mentally or with minimal jottings.