Question 37520
The times for going upstream is the same as downstream
{{{t(u) = t(d)}}}
Time equals distance divided by rate
rate of the river = 2 mph
rate of boat going downstream = 2 + b
rate of boat going upstream = 2 - b
{{{t(u) = 18 / (2 - b)}}}
{{{t(d) = 30 / (2 + b)}}}
{{{18 / (2 - b) = 30 / (2 + b)}}}
{{{18*(2 + b) = 30*(2 - b)}}}
{{{36 + 18b = 60 - 30b}}}
{{{48b = 24}}}
{{{b = 1/2}}}
Speed of boat in still water = 1/2 mph
check
{{{18 / (2 - .5) = 30 / (2 + .5)}}}
{{{18 / 1.5 = 30 / 2.5}}}
{{{180/15 = 300/25}}}
{{{12 = 12}}}
checks