Question

a boat can travel 30 miles upstream in the same amount of time you can travel 50 miles Downstream. If the speed of the current is 4 miles per hour, find the speed of the boat in still water.

Answer 1

The correct answer is 16mph.

Answer 2

Speed, S = Distance (d) / Time (t) => S= d/t => t= d/S

Let the speed of boat in still water be x mph

Resulting speed upstream = x-4 mph for a distance of 30 miles
Resulting speed downstream = x-4 mph for a distance of 50 miles

Time taken in both distances is equal.
Therefore,

30/(x-4) = 50/(x+4) => 30(x+4) = 50(x-4) => 30x+120 = 50x-200 => 120+200 = (50-30)x => 20x = 320 => x=320/20 = 16 mph

The speed of boat in still water is 16 mph.