A certain calculus teacher travels down Interstate 81 from Winchester to Harrisonburg at a constant rate of 60 mph. He returns over the same distance at a constant rate of 30 mph.
What was the average rate of speed over the entire
round trip?
Solution to Problem:
Answer is 40 mph
Solution:
The distance from Winchester to Harrisonburg is 60
miles,
but any distance will work.
Travelling at 60 mph, it would take 1 hour to travel
from
Winchester to Harrisonburg.
At 30 mph, it would take 2 hours to cover the 60
miles.
Therefore, it would take 3 hours to go the round trip
of 120
miles; so the average rate would be 40 mph!
Perhaps it is easier to see in a table:
| Rate | Time | Distance | |
|---|---|---|---|
| Winc. -> Harris. | 60 | 1 | 60 |
| Harris. -> Winc. | 30 | 2 | 60 |
| Roundtrip | 40 | 3 | 120 |
Correctly solved by:
| 1. Kirstine Wynn | Winchester, VA |
| 2. Jerry Putt | Greencastle, PA |
| 3. Court Pifer | James Madison University |
| 4. Bob Hearn | Winchester, VA |
| 5. David Powell | Winchester, VA |
| 6. Joanna Castiglia | Winchester, VA |
| 7. Richard Mocarski | Virginia Tech |
| 8. Ryan Throckmorton | Winchester, VA |
| 9. Joe Vance | Winchester, VA |
| 10. Elizabeth Cotter | Oak Hill, VA |
| 11. Erin McGinness | Winchester, VA |