Lisa drove 8 miles to pick up her friend Laurie, and then drove 11 miles to a mall at a speed 15 mph faster. If Lisa'a total travel time was 24 minutes, what was her speed on the trip to pick up Laurie?
Thank you!!
Let x = speed for first 8 miles.
Then x + 15 = speed for next 11 miles.
========================================
distance = rate x time
solve for time = d/r
For first 8 miles, time is
t = 8/x
For next 11 miles, time is
t = 11/(x+15).
If we add them we get 24 minutes which is 0.4 of an hour (24/60= 0.4)
(8/x) + [11/(x+15)] = 0.4
Solve for x.
I found x = between 10 and 15 minutes. Post your work if you get stuck.