2016 · Q24
A cyclist moves non-stop from A to B, a distance of 14 km, at a certain average speed. If his average speed reduces by 1 km per hour, he takes 20 minutes more to cover the same distance. The original average speed of the cyclist is
Elementary MathematicsTime, Speed and Distance
- A5 km/hour
- B6 km/hour
- C7 km/hour
- DNone of the above
Explanation
With original speed v km/h, the extra time is 14/(v−1) − 14/v = 1/3 h. This simplifies to 14/(v(v−1)) = 1/3, so v(v−1) = 42. Solving v²−v−42 = 0 gives v = 7 (the positive root), option C.