Question 209784
write 2 equations, 1 for the passenger plane
and 1 for the jet
{{{d[p] = r[p]*t[p]}}}
and
{{{d[j] = r[j]*t[j]}}}
given:
{{{r[j] = 2r[p]}}} mi/hr
{{{d[j] + d[p] = 2400}}} mi
{{{t[j] = 4}}} hrs
{{{t[p] = 4}}} hrs
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Now I can rewrite the equations:
{{{d[p] = r[p]*t[p]}}}
{{{d[p] = r[p]*4}}}
and
{{{d[j] = r[j]*t[j]}}}
{{{2400 - d[p] = 2*r[p]*4}}}
{{{-d[p] = 8r[p] - 2400}}}
{{{d[p] = 2400 - 8r[p]}}}
By substitution:
{{{4r[p] = 2400 - 8r[p]}}}
{{{12r[p] = 2400}}}
{{{r[p] = 200}}} mi/hr
and
{{{r[j] = 2r[p]}}}
{{{r[j] = 2*200}}}
{{{r[j] = 400}}} mi/hr
The speed of the passenger plane is 200 mi/hr
The speed of the jet is 400 mi/hr
check:
{{{d[p] = r[p]*t[p]}}}
{{{d[p] = 200*4}}}
{{{d[p] = 800}}}
and
{{{d[j] = r[j]*t[j]}}}
{{{d[j] = 400*4}}}
{{{d[j] = 1600}}}
{{{d[p] + d[j] = 800 + 1600}}}
{{{d[p] + d[j] = 2400}}} mi
OK