Using subtraction There are two ways to find the answer to subtraction calculations. First, you could start on the smaller number and count up to reach the bigger number. This works if the two ...

If you can subtract two 3-digit numbers from each other, then you can use the same method to subtract two 4-digit numbers. You use the same method, no matter how many digits are in the numbers.

For example, it took researchers two years recently to factor a 232-digit number, even with hundreds of parallel computers. That’s why the RSA algorithm is so effective.

According to this third-grade textbook, students must take about six steps (at minimum, depending how you count) to subtract just two numbers.

The idea behind using a number line for subtraction is that students get a visual representation of what subtraction is: figuring out the “distance” between two numbers.