Beat The GMAT

ajith · Sun Apr 01, 2007 11:11 pm

Boats in streams !, they can be very tricky at times!!!!

Okay, here is the basic theory behind it, there are 4 different speeds associated with these problems

1. Upstream Velocity -U
2. Downstream velocity - D
3. Speed of stream - S
4. Speed of boat in still water - B

Upstream velocity is the velocity at which a boat can travel upstream that is the difference between the velocity of the boat and speed of the stream

U= B-S -- (1)

Downstream velocity is the velocity at which a boat can travel downstream that is the sum of the velocity of the boat and speed of the stream

D= B+S --- (2)

(1) +(2) gives ,

2B= U+D
=>B= (U+D)/2

Similarly (2)-(1)
=> S = (D-U)/2

This is the only fundae you need to know while trying to solve a boat in stream problem

Question
A boat travels upstream at a speed of 4 mph and then downstream at a speed of 8 mph. What is the speed of the boat in still water and what is the speed of the stream?

Answer
When the downstream speed (D) and upstream (U) of a boat are given:
The speed of boat in still water, B = (D+U)/2 =6 Mph
Speed of the stream S = (D-U)/2 = 2 mph

That was easy , huh? , I am sure you will encounter more interesting problems once you look for it. If you have any problems with any of the Boat in stream problems feel free to post it here.

Happy learning
Ajith

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800GMAT · Mon Apr 02, 2007 9:17 pm

Thanks Ajith, for the initiative Very Happy

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ajith · Mon Apr 02, 2007 9:21 pm

you are always welcome,

Please suggest me a topic for I am lazy!!!

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ajith · Mon Apr 02, 2007 9:48 pm

" A boat travels 12 km upstream and back in 1 hour 45 minutes. If the speed of the current is 3km/hr throughout, find the speed of the boat in still water"

Please solve this to test your understanding, let me see who posts the answer first.

Statutory warning : This Problem may not be GMATish