Multiple choice

A person wishes to reach his destination $90$ km away in three hour but for the first half of the journey his speed was $20$ km/hr. His average speed for the rest of the journey should be

  1. $40$ km/hr
  2. $0.75$ km/min
  3. $1$ km/min
  4. $65$ km/hr
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Total distance = 90 km, total time = 3 hours. First half (45 km) at 20 km/hr takes 45/20 = 2.25 hours. Remaining time = 3 - 2.25 = 0.75 hours. Remaining distance = 45 km. Required speed = 45 / 0.75 = 60 km/hr. 60 km/hr = 1 km/min.

AI explanation

The first half of the journey is 45 km, and at 20 km/hr this takes 45/20 hours, which is 9/4 hours. The total time allowed is 3 hours, so the remaining time is 3 minus 9/4, giving 3/4 hours for the remaining 45 km. The required speed for the rest of the journey is 45 divided by 3/4, equaling 60 km/hr, which is equivalent to 1 km/min.

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