Math
posted by Felix Ferrer .
Please help me? A motorist takes a trip of 100 miles, traveling at 40 mph for the first 50 miles and 60 mph for the last 50 miles. What is the average speed in mph for the trip? The answer is not 50 mph.

distance = rate x time
Calculate time for each 50 mile increment. Add the times together to obtain total time.
then 100/total time = average rate. Post your work if you get stuck. 
i can't figure it out???

distance = rate x time
d for 40 mph vehicle = 50 mi = 40 mi/hr x time.
solve for time for 40 mph car = 50/40 = 5/4 hour.
d for 60 mph car = 50 mi = 60 mi/hr x t
solve for t for 60 mph car = 50/60 = 5/6 hr.
Add the times together.
5/4 + 5/6 = 1.250 + 0.833 = 2.083 hours total time.
distance traveled in total time = 100 miles. Average speed = 100 mi/2.083 hours = ??