Question 733323
You cannot take an average of average speeds to get
a combined average.
average speed = ( total distance ) / ( total time )
For the first 5 km she travelled on constant rate of 25 km/hour
{{{ 5 = 25*t }}}
{{{ t = 1/5 }}} hr
Then she traveled at constant rate of 15 km/hour as she climbed the 5 km hill
{{{ 5 = 15*t }}}
{{{ t = 1/3 }}} hr
She rode down the hill at a constant rate of 35 km/hour for the 5 km trip to the city center.
{{{ 5 = 35*t }}}
{{{ t = 1/7 }}} hr
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Total distance traveled was {{{ 3*5 = 15 }}} km
Total time for trip was {{{ 1/5 + 1/3 + 1/7 }}} hrs
{{{ 21/105 + 35/105 + 15/105 = 71/105 }}}
The total time for the trip was {{{ 71/105 = .676 }}} hrs
{{{ .676*60 = 40.57 }}} min
The is more than the 40 min for the tram, so she wasn't speeding