P130 (55)
A company uses a truck to deliver its products. To estimate costs, the manager models gas consumption by the function G(x) = 1/250 (1200/x +x) gal/mile, assuming that the truck is driven at a constant speed of x miles per hour, for x ≧ 5. The driver is paid $20 per hour to drive the truck 250miles,and gasoline costs $4 per gallon.
b. At what rate is the cost C(x) changing with respect to x when the truck is driven at 40 miles per hour?Is the cost increasing or decreasing at that speed?
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