Answer
$87.5$ miles per hour
Work Step by Step
At 3 PM, the train was around 275 miles from Denver.
By 5 PM, the train was 450 miles from Denver
The increase in distance from Denver is:
$=450-275=175$ miles
The elapsed time from 3 PM to 5 PM is 2 hours.
Thus, the average rate is:
$=\dfrac{175\text{ miles}}{2 \text{ hours}}=87.5$ miles per hour
