有道数学题帮忙解一下！！！

tracyyahoo

A bicyclist travels uphill from town A to town B for 2 hours at an average speed of 4 miles per hour and returns along the same road at an average speed of 6 miles per hour. What is the bicyclist’s average speed for the round trip, in miles per hour?

(a) 24/5
(b)  5
(c) 26/5
(d) 27/5
(e) 28/5

A is correct.. why???

pingyqi

往返总路程 8*2=16miles
共用时间：2+（2×4）/6=10/3

平均速度为二者相除

chebing

总路程是16，去时平均用时为8/4，回时平均时间为8/6则平均速度为16/（8/4+8/6）=24/5

azhongzhong

同意楼上答案应该是16/（8/4+8/6）=24/5 。选A.用总路程除以总时间，既得平均速度。

forgmat11

A is the 答案