Question

it took 2hrs

Answer 1

it took 2hrs for boat to go from a to b with current and 6hrs to go back against curent. assuming constant speed of boat in both directions, how long wil it take raft (with speed equal to speed of curent) to go from a to b?

Answer 2

let the boat (without any current) take 'x' hrs to reach from a to b
and the raft (with speed equal to speed of current) take 'y' hrs to reach from a to b
when current assist boat, total time taken was 2 hours, so x-y= 2
when current was against the boat, time taken was 6hrs , so x+y =6
find 'y' from here :)

Answer 3

that means x=y+2=6-y which means y=2? that cant be right though

Answer 4

yeah, i think i have overlooked something
speed = distance / time
here, distance is same
so,
speed * time will be constant
let their speed be 'a' and 'b'
so, (a+b)*2=(a-b)*6=distance =d
and you need, time taken by raft, = d/b
try it!

Answer 5

but d and b are both unknown. how can we solve it?

Answer 6

please help i still don't get it

Answer 7

so far,
a= speed of boat
b = sped of current
6a-6b = 2a + 2b meaning a = 2b

Answer 8

"d" is an arbitrary distance that is constant for all trips....let d=1
then
1/(a+b) = 2
1/(a-b) = 6

a = 2b
1/3b = 2
1/b = 6

--> b = 1/6
--> d/b = 6

it would take raft 6 hours

Answer 9

oh i get i now
thanks a lot