A hurricane is approaching the southern coast of Texas, and a rancher is planning to move 400 head of cattle 60 miles to higher ground to protect them from possible inland flooding that might occur.  His animal transport truck holds 20 head of cattle.  Traveling at 60 miles per hour, what is the total driving time, in hours, it will take to transport all of his cattle to higher ground?
Given the limited capacity of his transport vehicle (20 head of cattle), the 400 head of cattle will require 400/20=
<gadget id="calculator">400/20</gadget>
<output>20</output>
20 trips using his transport vehicle.
Traveling to the site at 60 mph for 60 miles it will take 60/60=
<gadget id="calculator">60/60</gadget>
<output>1</output>
1 hour to travel one-way.
Since each trip requires driving to and returning from the relocation site, each complete round trip will take 2*1=
<gadget id="calculator">2*1</gadget>
<output>2</output>
2 hours.
Thus, 20 complete trips will take 20*2=
<gadget id="calculator">20*2</gadget>
<output>40</output>
40 hours of driving time.

<result>40</result>