What type of mathematical strategy is used when decomposing 76 + 9 into 76 + 10 - 1?

The mathematical strategy used when decomposing 76 + 9 into 76 + 10 - 1 is known as compensation. This technique involves adjusting one of the numbers to make the arithmetic simpler. In this case, adding 10 instead of 9 makes it easier to calculate, and then subtracting 1 balances the equation back to the original sum.

Compensation is particularly useful in mental math, as it simplifies calculations by allowing for easier rounding or adjusting numbers while maintaining the same overall value. This method is widely employed for its efficiency in performing addition or subtraction in a more manageable form.