Question

9. Naveen rows in still water with a speed of 9 km/h to
cover a certain distance and to come back to the starting
point. Find his average speed for the whole journey, if
river is flowing with a speed of 3 km/h.​

Answer 1

Answer:

8 kmph

Step-by-step explanation:

formula (1) : time = distance/ speed

total distance : x (up) + x ( down ) = 2x km

speed in upstream : 9 - 3 = 6 kmph

speed in downstream : 9 + 3 = 12 kmph

upstream time t1 = x / 6 hrs

down stream time t2 = x / 12 hrs

total time = t1 + t2 = x/6 + x/12 = x/4

formula ( 2 ) : avg speed = total distance/ total time

avg speed = 2x / (x/4)

hence......avg speed = 8kmph