Multiple choice

A bike travels a distance of 200 km at a constant speed. If the speed of the bike is increased by 5 km an hour, the journey would have taken 2 h less. What is the speed of the bike?

  1. 30 km/h

  2. 25 km/h

  3. 20 km/h

  4. 15 km/h
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Let speed = s km/h, then time = 200/s hours. New speed = (s+5) km/h, new time = 200/(s+5) hours. The time difference is 2 hours: 200/s - 200/(s+5) = 2. Solving: 200(s+5 - s) = 2s(s+5), so 1000 = 2s² + 10s, giving s² + 5s - 500 = 0. Therefore (s+25)(s-20) = 0, so s = 20 km/h (speed must be positive).

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