AlgebraMediumMeaning of the slope's sign
Algebra practice question
The function d(t) = 480 − 60t gives the distance, in kilometres, between a train and its destination t hours after departure. Which statement is true?
- A. The train travels at 60 kilometres per hour and arrives after 8 hours.Correct
- B. The train travels at 480 kilometres per hour.
- C. The train is 60 kilometres from its destination at departure.
- D. The train's distance from its destination increases over time.
Answer: A. The train travels at 60 kilometres per hour and arrives after 8 hours.
The slope −60 means 60 km closer each hour; 480 ÷ 60 = 8 hours to reach 0.
Why the other answers are wrong
- B. The train travels at 480 kilometres per hour.
- 480 is the starting distance, not a speed.
- C. The train is 60 kilometres from its destination at departure.
- At t = 0 the distance is 480.
- D. The train's distance from its destination increases over time.
- The distance decreases (negative slope).
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