Chapter 3.2, Problem 11P

Tylishia says that she can calculate $324-197$ by adding 3 to both numbers and calculating $324-200$ instead.

1. Draw a number line (which need not be perfectly to scale) to help you explain why Tylishia’s method is valid.
2. Explain in another way why Tylishia’s method is valid.
3. Could you adapt Tylishia’s method to other subtraction problems, such as to the problem 183249? If so, give at least two more examples and show how to apply Tylishia’s method in each case.