Chapter 4.6, Problem 11CFU

(a)

To determine

To write: An equation that models the situation.

Answer to Problem 11CFU

  $\frac{3\left(60\right)+20}{3+x}=57.14$

Explanation of Solution

Given information: Interstate Commerce: When truckers are on long-haul drives, their driving logs must reflect their average speed. Average speed is the total distance driven divided by the total time spent driving. A trucker drove 3 hours on a freeway at 60 miles per hour and then drove 20 miles in the city. The trucker’s average speed was 57.14 miles per hour.

  

Calculation:

First Distance = $\left(\text{rate}\right)\left(\text{time}\right),$

So rate = $\frac{\text{distance}}{\text{time}}$

  ${\text{The Rate}}_{avg}=\frac{\text{Distance Sum}}{\text{Time Sum}}$

  $\frac{3\left(60\right)+20}{3+x}=57.14$

(a)

To determine

How long was the trucker driving in the city to the nearest hundredth of an hour?

Answer to Problem 11CFU

  $\simeq 0.50,$ Approximately half hour

Explanation of Solution

Given information: Interstate Commerce: When truckers are on long-haul drives, their driving logs must reflect their average speed. Average speed is the total distance driven divided by the total time spent driving. A trucker drove 3 hours on a freeway at 60 miles per hour and then drove 20 miles in the city. The trucker’s average speed was 57.14 miles per hour.

  

Calculation:

  $\frac{3\left(60\right)+20}{3+x}=57.14$

Multiply both sides by x + 3.

  $200=57.14\left(x+3\right)\to x\simeq \frac{1}{2}\simeq 0.50$

Approximately half hour