1. The problem states that Rob thinks of a number with one decimal place that rounds to 6 when rounded to the nearest whole number. 2. To round to 6, the number must be at least 5.5 and less than 6.5 because numbers from 5.5 up to (but not including) 6.5 round to 6. 3. Since the number has one decimal place, possible values are 5.5, 5.6, 5.7, 5.8, 5.9, 6.0, 6.1, 6.2, 6.3, and 6.4. 4. Any of these numbers will round to 6 when rounded to the nearest whole number. 5. Therefore, Rob's number could be any number in the set $$\{5.5, 5.6, 5.7, 5.8, 5.9, 6.0, 6.1, 6.2, 6.3, 6.4\}$$. Final answer: Rob's number could be any number with one decimal place between 5.5 and 6.4 inclusive.