A car and a truck were traveling to Asmara at constant speeds. The car overtook the truck when they were 420 km from Asmara. The car arrived in Asmara at 6:30 p.m. while the truck was still 120 km away. The truck arrived 8:30 p.m. What was the car speed?

1 Answer
David Drayer
Aug 28, 2016

The car's speed is 84 km/ hour.e

Explanation:

There may be better ways to solve this but breaking the problem into smaller pieces works.

First the truck traveled 120 Km in two hours.

Take 8:30 - 6:30 = 2 hours.

# 120 / 2# = 60 km/hr for the truck's speed.
Next take 420 km - 120 km = 300 km. this is the distance the truck traveled between the time the car passed the truck and when the truck was 120 km from the town.

The truck (assuming constant speed) travels at 60 km/ hr.
This can be used to find the time it took the car to travel to the town

# 300/ 60# = 5 hours

Now find the speed of the car by dividing distance by time.

420 km/ 5 hours = 84 km /hour.

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