Question 885443
Average speed is always ( total distance ) / ( total time )
{{{ 30 = 40t[1] }}}
{{{ t[1] = 3/4 }}}
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{{{ 30 = 60t[2] }}}
{{{ t[2] = 1/2 }}}
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Average speed  = {{{ ( 30 + 30 ) / ( 3/4 + 1/2 ) }}}
Average speed  = {{{ 60 / ( 5/4 ) }}}
Average speed = {{{ (4/5)*60 }}}
Average speed = 48 km/hr
The answer is b.