Question 874082
r = Kristin's speed and {{{r>50}}}.  Her speed was not given but the order relation was implied.  She will go 20 miles more than the truck to catchup.



_______________speed_________time_________distance
Kristin________r_____________t____________d+20
Truck__________50____________t____________d


The unknown variables for which to solve are t and d.  We must expect r is some constant rate, but this value was not given.


These equations are what the data allow for us:

{{{highlight_green(rt=d+20)}}} and {{{highlight_green(50t=d)}}}.


{{{rt-20=d}}};
Substituting, 
{{{50t=d}}}
{{{50t=rt-20}}}
{{{50t-rt=-20}}}
{{{rt-50t=20}}}
{{{t(r-50)=20}}}
{{{highlight(t=20/(r-50))}}} HOURS.


Again either equation, here choosing the truck,
{{{d=50t}}}
{{{d=50(20/(r-50))}}}
{{{highlight(d=100/(r-50))}}} MILES movement of the truck.
This means {{{20+100/(r-50)}}} miles movement for Kristin.


If you knew r for Kristin, then you can find values for t and d.