Question 226024
You have to write 2 equation, one for going and
one for coming back
To St. Paul:
{{{d[1] = r[1]*t[1]}}}
and coming back:
{{{d[2] = r[2]*t[2]}}}
Note that {{{d[1] = d[2]}}}, distance to St. Paul
given:
{{{r[1] = 200}}} mi/hr
{{{r[2] = 250}}} mi/hr
{{{t[1] = t[2] + 1}}} hrs
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Now I can rewrite the equations
{{{d = 200*(t[2] + 1)}}}
{{{d = 250t[2]}}}
They're both equal to {{{d}}}, so
{{{200*(t[2] + 1) = 250t[2]}}}
{{{200t[2] + 200 = 250t[2]}}}
{{{50t[2] = 200}}}
{{{t[2] = 4}}} hrs
and
{{{t[1] = t[2] + 1}}}
{{{t[1] = 4 + 1}}}
{{{t[1] = 5}}} hrs
Now I can solve for {{{d}}}
{{{d = 250t[2]}}}
{{{d = 250*4}}}
{{{d = 1000}}} 
St. Paul is 1000 mi away
check:
{{{d = 200*(t[2] + 1)}}}
{{{d = 200*(4 + 1)}}}
{{{d = 200*5}}}
{{{d = 1000}}}
OK