Sachi has 238 rocks in her collection. She finds 47 more rocks. Then she gives 159 rocks to her brother. She solves this equation 238 + 47 – 159 = r. She says, “I have 126 rocks left.”

1. Is Sachi’s answer reasonable?

2. How do you know?

3. Use estimation to check her work.

Show your work. There are three parts to your answer. Be sure to share your estimation strategy.