<PRE><B>Question 1069037</B>
In this type of problem, you can think of one of
the planes as standing still, and the other one
flying at the sum of their speeds
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Let {{{ s }}} = the speed in mi/hr of the slower plane
{{{ 2920 = ( s + s + 80 )*4 }}}
{{{ 2920 = ( 2s + 80 )*4 }}}
{{{ 2920 = 8s + 320 }}}
{{{ 8s = 2920 - 320 }}}
{{{ 8s = 2600 }}}
{{{ s = 325 }}}
and
{{{ s + 80 = 405 }}}
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Their speeds are
325 mi/hr and 405 mi/hr
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check:
{{{ d[1] = 325*4 }}}
{{{ d[1] = 1300 }}} mi
and
{{{ d[2] = 405*4 }}}
{{{ d[2] = 1620 }}}
and
{{{ d[1] + d[2] = 1300 + 1620 }}}
{{{ d[1] + d[2]  = 2920 }}}
OK </PRE>