Question 1179660
ust a different example of one of the frequent forms of travel-problems.


r, speed of boat if no current
c, speed of current
D, the large distance in T, the large time
d, the small distance in t, the small time

The unknown variables for this example are r and c.
The other variables are given.


{{{system(r+c=D/T,r-c=d/t)}}}


add corresponding parts

{{{2r=D/T+d/t}}}

{{{2r=(Dt+dT)/(Tt)}}}

{{{highlight_green(r=(Dt+dT)/(2Tt))}}}


subtract corresponding parts

{{{2c=D/T-d/t}}}

{{{2c=(Dt-dT)/(Tt)}}}

{{{highlight_green(c=(Dt-dT)/(2Tt))}}}


Problem description gives D=42, T=3.5, d=18, and t=3.
Using these to evaluate r and c,


{{{r=(42*3+18*3.5)/(2*3.5*3)}}}

{{{highlight(r=9)}}}

and

{{{c=(42*3-18*3.5)/(2*3.5*3)}}}

{{{highlight(c=3)}}}