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**Posts by Naru**

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gAr wrote:

Hi caymanisland,

The cost of the trip is an increasing function, so I assume that you mean that the cost must not increase beyond 30 $/hr.

I solved the following equation, which has one real solution:

x is the speed in km/hr, so that cost is 30 $/hr. Any speed less than that would result in lower $/hr as well as lower cost of the trip.

The answer in my textbook says it's 97.9km/h. Are you sure that's right?

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**Posts by Naru**