Question 981685
__________________rate__________time__________distance
Lake_______________20
RiverDown_________20+w__________t_____________2.9
RiverUp___________20-w__________t_____________2.5


RT=D uniform travel rates relationship for rate time distance


System of Equations:
{{{system((20+w)*t=2.9,(20-w)*t=2.5)}}}


ARITHMETIC OR ALGEBRA STEPS

Dividing one entire equation by the other entire equation will eliminate variable t.  (This is not the only possible method.)


{{{((20+w)t)/((20-w)t)=2.9/2.5}}}


{{{(20+w)/(20-w)=2.9/2.5}}}


{{{(20+w)(2.5)=(2.9)(20-w)}}}


{{{2.5w+20*2.5=2.9*20-2.9w}}}


{{{2.5w+2.9w=2.9*20-20*2.5}}}


{{{w(2.5+2.9)=20(2.9-2.5)}}}


{{{w(5.4)=20*(0.4)}}}


{{{w=(20*0.4)/5.4}}}


{{{w=20(4/54)}}}


{{{w=20(2/27)}}}


{{{w=40/27}}}


{{{highlight(w=1&13/27)}}}
about 1.48 mph   or  about  1.5 mph.