Instead of thinking about motion, subtraction can also be thought of as a distance between numbers. Here is a diagram that shows that \(7 - 3 = 4\text{.}\)
One of the values of this idea is that the distances do not change if you shift both numbers the same amount. This can sometimes allow you to think of the calculation in a slightly different manner that makes it easier to calculate. Here are two calculations where one is just slightly shifted from the other.
What were the two calculations? Which of the two calculations was easier to do? Why?
2.
There are two reasonable ways to calculate \(201 - 149\) by shifting the values. Draw the corresponding diagrams and compute the result using both approaches. Which one was easier for you? Why?
3.
Practice your mental arithmetic by performing the following calculations.
