+9481 A motorboat goes 5 miles upstream in the same time it requires to go 7 miles downstream. If the river flows at 2mph, find the speed of the boat in still water.
+129899 A motorboat goes 5 miles upstream in the same time it requires to go 7 miles downstream. If the river flows at 2mph, find the speed of the boat in still water.
Distance / Rate = Time
Let the rate of the boat in still water = R
Against the current the rate of the boat = R - 2
With the current the rate of the boat = R + 2
So......equate the time
5 / ( R - 2) = 7 / ( R + 2) cross-multiply
5 ( R + 2) = 7 (R - 2) simplify
5R + 10 = 7R - 14 rearrange as
24 = 2R
12 = R = 12 mph
The time it takes = 5 / [12- 2] = 5 / 10 = 1/2 hr
Well now I see what was wrong...my equation was this:
