Problem 11 · Working backwards · 3 points
Made by AI and not reviewed by a real person.
Rosa gave away 3 shells, then found 2 shells. She has 7 shells now. How many did she have at first?
- 9
- 6
- 5
- 8
- 12
Show a hint
- Start with the shells Rosa has now. Work backward through the story, undoing each change to find how many she had at first.
- Undo finding 2 shells first: 7 − 2 = 5. What must Rosa have had before she gave away 3 shells?
Show the answer and solution
Answer: D — 8
Before Rosa found 2 shells, she had 7 − 2 = 5 shells. Before she gave away 3 shells, she had 5 + 3 = 8 shells. So the answer is 8. The wrong answer 6 comes from starting with 7 and running the story forward: 7 − 3 + 2 = 6. But 7 is what Rosa has now, not what she had at first.