
John M. answered 04/08/16
Tutor
5.0
(87)
Certified Math Teacher with Statistics Masters
Basically you are calculating how long the boat will take to travel half a mile. Since it is traveling at 20 mph, or 20 miles in 1 hour, the boat won't need anywhere near an hour to travel the much shorter distance.
If we try to convert the speed to miles per minute, it'll be an odd fraction or a nasty decimal, so a better approach is to use a proportion.
If we rewrite 20 miles per 1 hour as 20 miles in 60 minutes, then we get the following proportion:
20/60 = 0.5/x
If you cross-multiply:
20x = 30
x = 1.5
Therefore, it takes 1.5 minutes to travel the half mile.