The table shows the volume of water in an emptying tank over time. A prediction for the volume at 105 seconds is 497 cm3. Is this a reasonable prediction? No, there is no recognizable pattern in the data from which to make a prediction. Yes, the first differences are all around –70, so a linear function is a good model. Subtracting 70 from 567 results in 497 cm3. No, the first differences are 15, so a linear function is a good model. Subtracting 15 from 567 results in 552 cm3. Yes, the average rate of change is about 8.