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Boats and Streams
A boat running upstream takes 640 min to cover a certain distance, while it takes 280 min to cover the same distance running down stream. What is the ratio between the speed of the boat and speed of water current respectively?
1) 23: 7
2) 22: 9
3) 23: 8
4) 23: 9
5) 23: 11
Read Solution (Total 6)
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- 4) 23 : 9
Let the speed of the boat=x and speed of the current=y
Relative speed in upstream=x-y and in downstream=x+y
Let the distance 'd' is to be covered in downstream and upstream, then
Time taken in upstream=d/(x-y)=640 or d=640(x-y) ----(i) and
Time taken in downstream=d/(x+y)=280 or d=280(x+y) ----(ii)
Comparing (i) & (ii), 640(x-y) = 280(x+y)
=> 16(x-y) = 7(x+y)
=> 16x -16y =7x -7y
=> 9x = 23y
=> x/y= 23/9 - 7 years agoHelpfull: Yes(35) No(0)
- [x+y]/640=[x-y]/280
x/y=23/9 - 7 years agoHelpfull: Yes(3) No(0)
- ans is 23:9
(640+280)/(640-280) - 6 years agoHelpfull: Yes(3) No(0)
- Answer 23 : 9
- 7 years agoHelpfull: Yes(2) No(0)
- Boat speed=0.5(64+28)=46
Boat speed=0.5(64-28)=18
Ratio=46/18=23/9 - 7 years agoHelpfull: Yes(2) No(2)
- always keep in mind "speed of the boat=(upstream+downstream)/2"
"speed of the stream=(us-ds)/2"
hence,speed of boat in terms of time=(920/2)=460
stream's speed=(360/2)=180
now ratio of boat and stream =(460/180)=23/9 - 6 years agoHelpfull: Yes(2) No(2)
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