Question

Suppose you run 4 miles from your house to a friends house at the speed of 7 miles per hour. When the time comes to return home, you are tired and walk the same 4 miles home at 3 miles per hour.

(The first question is how long did you spend running to your friends house)

Answer 1

9514 1404 393

Answer:

a. 0.6 h

b. 1.3 h

c. C -- No

d. 4.2 mi/h

Explanation:

a. The relationship between time (t), speed (s), and distance (d) is ...

t = d/s

The time spent running 4 miles at 7 miles per hour is ...

t = (4 mi)/(7 mi/h) = (4/7) h ≈ 0.6 h

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b. The time spent walking home is ...

t = (4 mi)/(3 mi/h) = 4/3 h ≈ 1.3 h

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c. C -- No, less time is spent at 7 mi/h

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d. The average speed is ...

s = d/t = (4 mi +4 mi)/(4/7 h +4/3 h) = (8 mi)/(40/21 h) = 4.2 mi/h