Question 1051684
Average speed = [ total distance ] / [ total time ]
Let {{{ d }}} = the one-way distance Boston to NY
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Boston to NY:
{{{ t[1] = d/40 }}}
NY to Boston:
{{{ t[2] = d/60 }}}
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Average speed  = {{{ 2d / ( t[1] + t[2] ) }}}
{{{ 2d / ( d/40 + d/60 ) }}}
{{{ (d/d)*( 2/( 1/40 + 1/60 )) }}}
Multiply top and bottom by {{{ 120 }}}
{{{ 240 / ( 3 + 2 ) }}}
{{{ 240/5 = 48 }}}
the average speed is 48 mi/hr