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A family is on a road trip. The speed limit during the first 115 miles of the trip is 55 mph, and the speed limit during the last 165 miles is 70 mph. How many miles per hour over the speed limits must they drive in order to arrive at their destination in 4 hours?

Sep 1, 2020

#1
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A family is on a road trip. The speed limit during the first 115 miles of the trip is 55 mph, and the speed limit during the last 165 miles is 70 mph. How many miles per hour over the speed limits must they drive in order to arrive at their destination in 4 hours?

Hello Guest!

$$\large \frac{115}{55+x}+\frac{165}{70+x}=4$$

$$x=6.9601$$

6.96 miles per hour over the speed limits must they drive in order to arrive at their destination in 4 hours.

!

Sep 1, 2020
edited by asinus  Sep 1, 2020
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[165/(70)  +  115/(S+55)] =4, solve for S

S = 15 mph - they must drive over speed limit, but ONLY for for the first leg of 115 miles. They do not need to drive over the speed limit in the 2nd leg of 165 miles.

Sep 2, 2020