An impatient driver, wanting to save time, drives along a city bypass at an average speed of 115 km/h where the speed limit is 90.0 km/h. If the bypass is 18.0 km long, how much time (in minutes) does the driver save by breaking the speed limit? (By the way, the driver consumes about 20% more fuel at the higher speed.)
The time it will take at 90 and 115 km/h:
"t_1=\\frac{18}{90}=0.2\\text{ h},\\\\\\space\\\\\nt_1=\\frac{18}{115}=0.16\\text{ h},\\\\\\space\\\\\n\\Delta t=0.2-0.16=0.04\\text{ h, or 2.4 min}."
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