Charlie rides his bicycle down a hill at 30 kilometers per hour. Then he turns around and rides back up the hill at 6 kilometers per hour to his starting point. What is Charlie's average speed for the whole trip down and back up the hill?
+36916 The distance is the same d = rate * time it is the TIME that is different
d = 30 k/h * t1
d = 6k/h * t2 and they are equal
d/30 = t1 and d/6 =t2
Total distance is 2 d
2d = Average *(t1 +t2)
2d = average * (d/30 + d/6)
2d = average ( (d+5d)/30)
2d = average * (6d/30)
2d * 30/6d = average
2*30/6 = average = 10 k/hr
