Question 1191070

Lauren's boat can go 9 miles per hour in still water. How far downstream can Lauren go if the river has a current of 3 miles per hour and she must be back in 4 hours.
<pre>Let distance back and forth be D
Then time Lauren will take to travel downstream is: {{{matrix(1,3, D/(9 + 3), or, D/12)}}}
Also, time Lauren will take to return upstream is: {{{matrix(1,3, D/(9 - 3), or, D/6)}}}
With Lauren taking 4 hours to complete round-trip, we get the following TIME equation: {{{matrix(1,3, D/12 + D/6, "=", 4)}}}
D + 2D = 48 ------- Multiplying by LCD, 12
3D = 48
Distance Lauren can travel downstream and back, in 4 hours, or {{{highlight_green(matrix(1,6, D, "=", 48/3, "=", 16, miles))}}}</pre>