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A biker travels the 120 mi from New York , NY to Wilmington, DE in 8 hours. A bus, a truck, and a rider on a horse take the same route as the biker. At what speed does each of them travel if it takes them 2 hours, 2.5 hours, and 18.75 hours respectively to reach Wilmington? Do the speed and the time vary directly or inversely proportional when the same distance is traveled? Explain why.

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Answer:

First, remember the relation:

Distance = Speed*Time.

We know that the distance is 120mi.

A) For the biker we know that:

Time  = 8hours.

Speed = Distance/Time = 120mi/8h = 15 mi/h.

B) For the bus we know that:

Time = 2 hours.

Speed = Distance/Time = 120mi/2h = 60 mi/h.

C) For the truck we know that:

Time = 2.5 hours.

Speed = Distance/Time = 120mi/2.5h = 48 mi/h.

D) For the rider on a horse we know that:

Time = 18.75 hours.

Speed = Distance/Time = 120mi/18.75h = 6.4 mi/h.

E) The equation for the speed is:

Speed = Distance/Time.

You can see that time is in the denominator, this means that if for a fixed distance, the time increases, then the denominator increases, which would imply that the speed decreases.

Then the speed is inversely proportional to the time when the distance is fixed.

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