To find the average speed for each route, we can use the formula for speed, which is:
\[ \text{Speed} = \frac{\text{Distance}}{\text{Time}} \]
For Route 1:
- Distance = 400 miles
- Time = 8 hours
Calculating the average speed:
\[ \text{Speed}_1 = \frac{400 \text{ miles}}{8 \text{ hours}} = 50 \text{ mph} \]
For Route 2:
- Distance = 420 miles
- Time = 7 hours
Calculating the average speed:
\[ \text{Speed}_2 = \frac{420 \text{ miles}}{7 \text{ hours}} = 60 \text{ mph} \]
Now, to find how much higher the average speed is on the faster route (Route 2) compared to Route 1:
\[ \text{Difference in speed} = \text{Speed}_2 - \text{Speed}_1 = 60 \text{ mph} - 50 \text{ mph} = 10 \text{ mph} \]
Thus, the average speed of Route 2 is 10 mph higher than that of Route 1.
The answer is 10 mph.