Question

Answer this quickly please!

Lisa started to drive from Boston to Washington, DC, which is 440 miles away, at 8:00 AM. For the first four hours of her trip, Lisa was driving at a speed of 50 mph. What was her average speed during the second part of the trip, if she reached Washington at 4:00 PM?

Answer 1

`\bar v = 60\,mph`

Explanation:

The distance travelled by Lisa in the first four hours of her trip is:

`\Delta s = \left(50\,mph)\cdot (4\,h)`

`\Delta s = 200\,mi`

The distance remaining and her average speed are, respectively:

`\Delta s_(R) = 440\,mi - 200\,mi`

`\Delta s_(R) = 240\,mi`

`\bar v = (240\,mi)/(4\,h)`

`\bar v = 60\,mph`