Distance covered by a boat in 5 hours = 36kmRate upstream of boat = 365=7.2kmphSpeed of the stream=2.4kmph∴speed of the boat in stil water = (7.2+2.4)kmph=9.6kmph∴Rate downstream of the boat = (9.6+2.4)kmph=12kmph∴Time taken in covering 78 km distance = 7812=6.5hours.
Suppose he moves 4 km downstream in x hours.Then , Speed downstream = (4x)km/hrSpeed upstream = (3x)km/hr∴48(3x)+48(4x)=14orx=12So,Speed downstream = 7 km/hrSpeed uptream = 6 km/hrRate of the stream = 12(8−6)km/hr=1km/hr
GivenSpeed of boat in downstream = 15 km/hSpeed of current = 3 km/hSpeed of boat in still water = 12 km/hTime taken at upstream = 1512−3=159h=1h 40minTime taken at downstream = 1512+3=1htotal time = 2 h 40 min
According to questionSpeed of current y=4km/hDistance = 12kmSpeed in upstream = (x−y)km/hr.Here x is speed of boat in still water = DistanceTimex−4=1255x−20=125x=32x=6.4km/hrSpeed in downstream = (x+y)=6.4+4=10.4km/h∴Time = DistanceSpeed Time = 1510.4=150104=1hour26713minutes
According to questionDownstream speed = x+yUpstream speed = x−ySpeed = DistanceTime∴x+y=DT................(i)x+y=D2T................(ii)Solve equation (i) and (ii) x = 3D4T,y=D4T∴xy=3D4T×4TD=31=3:1Downstream (D)Upstream (U)T→1:2S→2:1SB=SD + SU2=2+12=32SC=SD−SU2=2−12=12SB:SC=32:12=3:1