Question 895513
Average speed is always:
( total distance traveled ) / ( total time spent traveling )
Let {{{ d }}} = the one-way distance to the store
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From home to store:
{{{ d = 6*( 20/60 ) }}}
{{{ d = 6*( 1/3 ) }}}
{{{ d = 2 }}} mi
( note that I converted minutes to hours )
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Let {{{ t }}} = time in hours to get home
From store to home:
{{{ d = 12t }}}
{{{ 2 = 12t }}}
{{{ t = 1/6 }}} hr
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Her average speed is:
{{{ ( 2 + 2 ) / ( 1/3 + 1/6 ) }}}
{{{ 4 / ( 2/6 + 1/6 ) }}}
{{{ 4 / ( 3/6 ) }}}
{{{ 4 / ( 1/2 ) = 8 }}} mi/hr