What is the purpose of the opposite change rule method in mathematics?

The opposite change rule method in mathematics is designed to help make mental calculations simpler and more manageable. This method involves adjusting one number upward while simultaneously adjusting another number downward in a way that keeps the overall total the same. This technique often results in "friendly numbers," which are easier to work with mentally.

For instance, if you're asked to add two numbers like 49 + 6, rather than calculating it directly, you could increase 49 to 50 (a rounded number that's easier to work with) by adding 1, and then decrease 6 by 1 to still keep the total the same. This allows for a straightforward mental calculation of 50 + 5, which equals 55.

The purpose of this method is to enable students to utilize mental math strategies that enhance their number sense and improve their ability to perform calculations efficiently without a strict reliance on paper and pencil.