<PRE><B>Question 633370</B>
Let {{{ p }}} = the speed of the plane in still air
{{{ p + 40 }}} = speed of plane from Orlando to Denver in mi/hr
{{{ p - 40 }}} = speed of plane from Denver to Orlando in mi/hr
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1st trip:
{{{ d = ( p + 40 )*5 }}}
2nd trip:
{{{ d = ( p - 40 )*6 }}}
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By substitution:
{{{ (p + 40 )*5 = ( p - 40 )*6 }}}
{{{ 5p + 200 = 6p - 240 }}}
{{{ p = 440 }}}
440 mi/hr is the speed of the plane in still air
check:
{{{ d = ( 440 + 40 )*5 }}}
{{{ d = 480*5 }}}
{{{ d = 2400 }}} mi
and
{{{ 2400 = ( p - 40 )*6 }}}
{{{ 2400 = 6p - 240 }}}
{{{ 6p = 2640 }}}
{{{ p = 440 }}} mi/hr
OK</PRE>