John and Anne want to calculate 253 - 99 by first calculating
253 - 100 = 153
John says that they must now subtract 1 from 153, but Anne says that they must add 1 to 153.
a. Draw a number line (which need not be perfectly to scale) to help you explain who is right and why. Do not just say which answer is numberically correct; use the number line to help you explain why the answer must be correct.
b. Explain in another way who is right and why.