“Lewis and Carol travel together on a road from A to B, then return on the same road, with the entire trip taking 3 hours. Sometimes that road goes uphill, sometimes downhill, and sometimes it is level. When the road goes uphill, their rate is 40 mph; downhill their rate is 60 mph; on level road, their rate is *x* mph.”

Even if you were given a numerical value for *x*, the distance from A to B would (in most cases) not be uniquely determined. But there is one value for *x* that would determine that distance uniquely. Compute this value of *x* [Note: uphill going is downhill returning!]

Credits – Southern California ARML, Oct. 2009, Team round

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