Question 899613
The average speed is: 
( total distance traveled ) / ( total time of travel )
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{{{ d[1] = 10*1 }}}
{{{ d[1] = 10 }}} km
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{{{ d[2] = 13*2 }}}
{{{ d[2] = 26 }}}
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{{{ d[3] = 11*1 }}}
{{{ d[3] = 11 }}} km
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{{{ d[1] + d[2] + d[3] = 10 + 26 + 11 }}}
{{{ d[1] + d[2] + d[3] = 47 }}}
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total time = {{{ 1 + 2 + 1 }}}
total time = {{{ 4 }}} hrs
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{{{ 47 / 4 = 11.75 }}} km/hr
I don't see how it could be 15 km/hr
with the given numbers