Multiple choice

A train travels a distance of 300 km. at constant speed. If the speed of the train is increased by 5 km. an hour, the journey would have taken 2 hours less. Find the original speed of the train.

  1. 30 km./hr.

  2. 25 km./hr.

  3. 24 km./hr.

  4. 20 km./hr.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let v be original speed. Time = distance/speed, so 300/v - 300/(v+5) = 2. Solving: 300(v+5 - v)/v(v+5) = 2, giving 1500 = 2v² + 10v, or v² + 5v - 750 = 0. Factoring: (v+30)(v-25) = 0, so v = 25 km/hr. Check: 300/25 = 12 hr, 300/30 = 10 hr, difference is 2 hr. Option A (30) gives original, not the increased speed.

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