Question 570740
Average speed is always ( total distance traveled ) / ( total time it takes )
I will say that the towns are {{{ d }}} miles apart
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Time going from A to B:
{{{ d/x }}}
Time going from B to A:
{{{ d/y }}}
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Ave speed = {{{ (2d) / ( d/x + d/y ) }}}
Divide top and bottom by {{{d}}}
Ave speed = {{{ 2 / ( 1/x + 1/y ) }}}
Multiply top and bottom by {{{ x*y }}}
Ave speed = {{{ (2*x*y) / ( x + y ) }}}
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If the round trip takes {{{ t }}} hrs,
{{{ (2d)/t = (2*x*y) / ( x + y ) }}}
Distance apart is {{{ d = (x*y*t) / ( x + y ) }}}