Question

A boat takes 8 hours to sail from one place to another and back to the starting point. if the speed of the river is4kmph and the spead of the boat is 8kmph, find the distance

Answer 1

first when river is down stream for boat then speed = 8+4 =12 km/hr

and when boat come back then river is upstream for boat then speed =  8-4 = 4km/hr

total distance we assume  "2y" m.
and total time in travel distance is 8 hour

assume time taken ,when boat travel one place to another = x = y/12 hour--(i)

and when boat come back = 8 - x = y/4---(ii)

equation (i) + (ii)
8 = y/12 + y+4
8 = 4y/12
y = 24 km

so total distance = 2y = 2 x 12 = 24 km

i hope it will help you
regards