Homework Help: Math

Posted by Leigh on Friday, February 12, 2010 at 8:33pm.

A semi-truck travels on a paved road for 2 hours at an average speed of 20 miles per hour faster than it travels on a dirt road. The time spent on the dirt road is 3 hours. If the entire trip is 200 miles, how fast is the truck traveling on the dirt road?

Math - Anonymous, Saturday, February 13, 2010 at 12:50am
Use d = r * t for both the paved and the dirt roads. Use x for the unknown speed on the dirt road.

For the paved road, use d1 (distance 1):
d1 = r * t
d1 = (x + 20) * 3
so
d1 = 3(x + 20)

For the dirt road, use d2 (distance 2):
d2 = r * t
d2 = x * 3
so
d2 = 3x

Also, you know that the distance traveled on the paved road, d1, and the distance traveled on the dirt road, d2, sum to 200 miles. Thus, you know:
d1 + d2 = 200

See if you can take it from there.

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