When asked to compute 423- 157, a student wrote the following:

4-

30-

34-

300

266

• Explain why the student's technique is valid usingtraditional expanded notation.
• Think about how you might apply Pat's technique to calculate 547 - 198, verify your answer using a place value drawing, and check the answer using theungroup first where neededmethod, subtracting from left to right.