Question 197729
I have an equation for each one
{{{d[t] = r[t]*t[t]}}}
and
{{{d[d] = r[d]*t[d]}}}
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given:
{{{r[t] = r[d] + 3}}} mi/hr
{{{t[t] = t[d]}}} (I'll call them both {{{t}}})
{{{d[t] = 200}}} mi
{{{d[d] = 188}}} mi
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What is Thelma's average driving speed?
{{{d[t] = r[t]*t[t]}}}
{{{200 = r[t]*t}}}
{{{200 = (r[d] + 3)*t}}}
and
{{{d[d] = r[d]*t[d]}}}
{{{188 = r[d]*t}}}
{{{r[d] = 188/t}}}
Substituting,
{{{200 = (188/t + 3)*t}}}
{{{200 = 188 + 3t}}}
{{{3t = 12}}}
{{{t = 4}}} hr
Substituting,
{{{200 = r[t]*t}}}
{{{r[t] = 200/4}}}
{{{r[t] = 50}}}
Thelma's average driving speed was 50 mi/hr
check:
{{{r[t] = r[d] + 3}}} mi/hr
{{{50 = r[d] + 3}}}
{{{r[d] = 47}}} mi/hr
{{{d[d] = r[d]*t[d]}}}
{{{188 = 47*4}}}
{{{188 = 188}}}
and
{{{d[t] = r[t]*t[t]}}}
{{{200 = 50*4}}}
{{{200 = 200}}}
OK