To find out how far Jimmy's truck travels after seven revolutions of the tires, we first need to calculate the circumference of one tire, which represents the distance traveled in one complete revolution.
The formula for the circumference \( C \) of a circle is given by:
\[ C = 2 \pi r \]
where \( r \) is the radius of the tire.
Given that the radius \( r \) of the tires is 39 inches and using \( \pi \approx 3.14 \), we can calculate the circumference as follows:
\[ C = 2 \times 3.14 \times 39 \]
Calculating this step-by-step:
\[ C = 6.28 \times 39 \] \[ C = 245.92 \text{ inches} \]
Now, since the truck makes seven revolutions, we multiply the circumference by the number of revolutions to find the total distance traveled:
\[ \text{Total Distance} = 245.92 \text{ inches} \times 7 \] \[ \text{Total Distance} = 1721.44 \text{ inches} \]
Next, we need to convert inches into feet. Since there are 12 inches in a foot, we divide the total distance in inches by 12:
\[ \text{Total Distance in feet} = \frac{1721.44}{12} \] \[ \text{Total Distance in feet} = 143.4533 \text{ feet} \]
Rounding to two decimal places, the truck travels approximately 143.45 feet after seven revolutions.