+101 A boat travels 14 km/h in still water. If this boat goes upstream in a river flowing at a rate of 4 km/h, for 3 km, and then returns back downstream to its starting point, what is the average speed for the whole trip in km/h?
+118677 It goes upstream at 10km/hour for 3 km so that takes 0.3 of an hour
It goes downstream tat 18km/hour for 3km so that takes 1/6 of an hour
Total distance = 6km total time = (18+10)minutes = 28/60 hour
ave speed = \(6\div \frac{28}{60}=12\frac{6}{7}\;km/hour\)
Sorry guest answerers, I was correcting my answerer without seeing that you had already done so.
I did make a very careless error and I thank you for correcting it.
14 - 4 ==10 km/h - its speed upstream
3 km / 10 km/h ==3/10 x 60 ==18 minutes going upstream
14 + 4 ==18 km/h - its speed downstream
3 km/18 km/h ==1/6 x 60 ==10 minutes going downstream
Average speed ==total distance travelled / time
== [3 * 2] / [18 + 10] / 60
== 6 / [28 / 60]
== 6 * 60 / 28 ==360 / 28 ==12 6/7 km/h
