A boat travels for three hours with a current of 3 mph and then return

Question

A boat travels for three hours with a current of 3 mph and then returns the same distance against the current in four hours. What is the boat's speed in calm water?

A. 19mph
B. 20mph
C. 21mph
D. 22mph
E. 23mph

How far did the boat travel one way?

srijay007 · Answer

Let velocity of boat in calm water be V
(V+3)*3 = (V-3)*4 ... same distance
Solving V= 21

Anonymous · Answer

The distance travelled will always be fixed.

So distance = 3mph * 3h = 9miles

Speed will be (s+3)*3 = (s-3)*4 assuming the current does not change direction and stays constant

so S = 21mph

ywilfred · Answer

Sorry, once again, I forgot to log in before replying. The 'guest' was actually me. :oops:

venksune · Answer

Let B be the velocity of the boat and U be the velocity of the stream.

(B+U) x 3 = (B-U) x 4

(3+B) x 3 = (B-3)x 4

9+3B=4B-12

B=21

The boat travelled (21-3) x 4hrs = 72 miles one way.

ywilfred · Answer

Venksune, you got the distance right... I overlooked the question when I calculated the distance travelled... :oops:

ian7777 · Answer

same answers and methods as everyone else:

3(r+3)=4(r-3)
r=21
D=72

mba · Answer

Ans,
21mph speed.
72miles distance.

(Approach, same as adopted by others)

TheNona · Answer

Can any body elborate more , please ? Thanks in advance

Narenn · Answer

Let the speed in still water be x
Speed of stream = 3

So
Speed while going downstream = x+3
Time while going downstream = 3
Speed while going upstream = x-3
Time while going upstream = 4

Since distance traveled through both ways is same and time ratio being  \frac{3}{4} , the speed ratio must be  \frac{4}{3}

\frac{Speed downstream}{Speed upstream}  =  \frac{4}{3}

\frac{x+3}{x-3}  =  \frac{4}{3}  ------> 3x + 9 = 4x - 12 ----------> x=21

Speed in still water = 21

Distance = Speed X Time
Distance = (x+3)3 = 24 X 3 = 72
or
Distance = (x-3)4 = 18 X 4 = 72

Regards,

Narenn

hero_with_1000_faces · Answer

is this GMAT Type question ?

Abhishek009 · Answer

Certainly , boat in still and flowing river is part of GMAT syllabus.

JeffTargetTestPrep · Answer

Let r = the boat’s speed in calm water. So we have the rate going with the current is (r + 3) and against is (r - 3). We know that the boat traveled the same distance when traveling with the current as when traveling against the current; thus:

(r + 3) x 3 = (r - 3) x 4

3r + 9 = 4r - 12

21 = r

Thus the boat’s speed in calm water is 21 mph, and the boat travels (21 + 3) x 3 = 72 miles one way.

bumpbot · Answer

Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.

A boat travels for three hours with a current of 3 mph and then return

Prep Toolkit

Top 5 GMAT Debrief Videos

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards

GMAT Problem Solving (PS) Questions

A boat travels for three hours with a current of 3 mph and then return

Prep Toolkit

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards