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This problem provides a great opportunity to introduce the concept of representing operations on unknown numbers algebraically. It leads to work on inverse operations and solving simple linear equations. When first shown the interactivity, students may be amazed and astonished that it can always work out the starting number. The intention is to provoke their curiosity so they become
determined to explain the mystery.
Finishing Number | Starting Number |
11 | 5 |
17 | 8 |
3 | 1 |
23 | 11 |
14 | 6.5 |