Aptitude - Boats and Streams - Discussion

I got it. 8*5+4=44.

Fractions!

8hr48min we need to convert 8hr48min in terms of only hr because we are required to compare 8hr48min to 4hr....and in 4hr there are no unit of any min therefore we have to convert 8hr48min in only hr ok....and 8 is already given in hr....
so that we will convert only 48min in terms of hr
60min=1hr
1min=1/60
similarly...
60min=1hr
1min=1/60
48min=(1/60)*48=48/60hr

[8(48/60)]hr=8(4/5)=8*5+4=40+4=44

@Binza

your explantation is not correct. This is not train problem to take like that. Speed of boat supported by extra speed of water current when down stream and reduced in up stream.

@ prasanth
binza concept is correct,but i still does't understand the avg?????

As distance is same formula will be upstream speed X time1 =downstream speed x time 2

Time 1 =8+4/5=44/5 hrs,time2=4 hrs

(U-V)*44/5=(U+V)*4
44U-44V=20U+20V
24U-64V=0
24U=64V
U/V=64/24
=8/3.

I got this trick

as y =speed of boat in downstream
so it ll be equal to = speed of boat + speed of water
x= speed of boat in upstream
so it ll = speed of boat - speed of water
so y +x/2 =(spd of boat)
simillerly y - x/2 =speed of water

So thats way they took this ratio.

Its the ratio between speed of the upstream and speed of the down stream.

Formula is (a+b)/2:(a-b)/2.

See the formula you will get it.

@sangu
Thank u a lot..

Let the man's rate upstream be U kmph and that downstream be V kmph.

Then, distance covered upstream in 8 hrs 48 min = Distance covered downstream in 4 hrs.

[U*8*48/60] = [V*4] [BECAUSE 1 MINUTE=60SECONDS]
[U*8*4/5] = [4V]
[U*44/5] = [4V]
44/5 U = 4V

THEN, USE THE FORMULA-----If the speed of the boat in still water is U km/hr and the stream of the boat is V km/hr then.

speed downstream = (u+v)km/hr
speed up stream = (u+v)km/hr

so, our U= 44/5 COME AND V= 4 COME

NOW, [U+V]/[U-V]
[44/5+4] / [44/5-4]
[44+20] / [44-20]
64/24,
8/3,
8:3 ANS

Thanks Bindu.