Question 387690
Rate*Time=Distance
{{{R*t=D}}}
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Let the boat rate be {{{B}}}, the current rate {{{C}}}.
With the current,
{{{(B+C)2=320}}}
1.{{{B+C=160}}}
Against the current,
{{{(B-C)4=320}}}
2.{{{B-C=80}}}
Add the equations together,
{{{B+C+B-C=160+80}}}
{{{2B=240}}}
{{{highlight(B=120)}}}kph
Then use either equation to solve for {{{C}}}.
{{{120+C=160}}}
{{{highlight(C=40)}}}kph