Posted by **Felix Ferrer** on Tuesday, October 2, 2007 at 6:15pm.

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.

- Math -
**DrBob222**, Tuesday, October 2, 2007 at 6:26pm
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.

- Math -
**Felix Ferrer**, Tuesday, October 2, 2007 at 7:09pm
i can't figure it out???

- Math -
**DrBob222**, Tuesday, October 2, 2007 at 7:24pm
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 = ??

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