Answer:
15 miles per hour
Explanation:
Average Speed is:
Average Speed = Total Distance/Total Time
Going uphill, she took 12 minuets, that is hours is 12/60 = 0.2 hours
We know D = RT, Distance = Rate(speed) * Time
Thus,
D = 10mph * 0.2 hr = 2 miles
So, total distance (uphill and downhill) = 2 + 2 = 4 miles
Downhill the time she took is
D = RT
2miles = 30mph * T
T = 2/30 = 1/15 hours = 1/15 * 60 = 4 minutes
Hence total time is 12 + 4 = 16 minutes
Note: 16 minutes = 16/60 = 4/15 hours
Now
Average Speed = Total Distance/Total Time
Average Speed = 4 miles/ 4/15 hours = 15 mph