Multiple choice

An airplane travelled a distance d in t hours (where t > 1) and arrived one hour late. The airplane would have arrived on time, if it had travelled at the speed of

  1. t – 1

  2. d/t – 1

  3. d/t + 1

  4. d/(t – 1)

  5. d/(t + 1)
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D Correct answer
Explanation

The current speed is d/t. To arrive on time (one hour earlier), the airplane must cover distance d in (t - 1) hours. The required speed is distance / new time = d / (t - 1).

AI explanation

Using the basic formula time equals distance divided by speed, the usual time to arrive on time is (t minus 1) hours because the airplane was one hour late. The required speed to arrive exactly on time is the distance d divided by this usual time. Therefore, the necessary speed is d divided by (t minus 1).

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