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WizakoBaskar
pv8172
The total time taken by a boat to travel \(x\) km downstream and \((x - 5)\) km upstream was 569.2 minutes. If the difference between the speed of the boat downstream and that in upstream is 3 kmph and the respective ratio between speed of boat in still water and speed of water current was (9 : 1), what is the value of x?

A) 63.8
B) 34.4
C) 29.4
D) 68.8
E) 62.5


Let the speed of the boat in still water be B km/hr
Let the speed of water current be S km/hr.

Downstream speed = B + S
Upstream speed = B - S

Given data 1: Difference between speed of boat downstream and that upstream = 3 km/hr
So, (B + S) - (B - S) = 3
Or 2S = 3 or S = 1.5 km/hr.

Given data 2: Ratio between speed of boat in still water and speed of water current was (9 : 1)
B : S = 9 : 1
If S = 1.5 km/hr, B = 9*1.5 = 13.5 km/hr

The boat travels x km downstream. i.e., the boat travels x km @ (13.5 + 1.5) = 15 km/hr
The boat travel (x - 5) km upstream. i.e., the boat travels (x - 5)km @ (13.5 - 1.5) = 12 km/hr

Given data 3: Total time taken = 569.2 minutes = \(\frac{569.2}{60}\) hours.

Total time taken = \(\frac{x}{15} + \frac{{x - 5}}{12} = \frac{569.2}{60}\)
\(\frac{{4x + 5x - 75}}{60} = \frac{569.2}{60}\)
\(\frac{{9x - 75}}{60} = \frac{569.2}{60}\)
or 9x - 75 = 569.2
So, 9x = 644.2
x = 71.57

None of the answer choices match. Could you please check the answer options?

Those are the only available options.
I think author did some mistake in giving options.
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chetan2u
WizakoBaskar
pv8172
The total time taken by a boat to travel \(x\) km downstream and \((x - 5)\) km upstream was 569.2 minutes. If the difference between the speed of the boat downstream and that in upstream is 3 kmph and the respective ratio between speed of boat in still water and speed of water current was (9 : 1), what is the value of x?

A) 63.8
B) 34.4
C) 29.4
D) 68.8
E) 62.5


Let the speed of the boat in still water be B km/hr
Let the speed of water current be S km/hr.

Downstream speed = B + S
Upstream speed = B - S

Given data 1: Difference between speed of boat downstream and that upstream = 3 km/hr
So, (B + S) - (B - S) = 3
Or 2S = 3 or S = 1.5 km/hr.

Given data 2: Ratio between speed of boat in still water and speed of water current was (9 : 1)
B : S = 9 : 1
If S = 1.5 km/hr, B = 9*1.5 = 13.5 km/hr

The boat travels x km downstream. i.e., the boat travels x km @ (13.5 + 1.5) = 15 km/hr
The boat travel (x - 5) km upstream. i.e., the boat travels (x - 5)km @ (13.5 - 1.5) = 12 km/hr

Given data 3: Total time taken = 569.2 minutes = \(\frac{569.2}{60}\) hours.

Total time taken = \(\frac{x}{15} + \frac{{x - 5}}{12} = \frac{569.2}{60}\)
\(\frac{{4x + 5x - 75}}{60} = \frac{569.2}{60}\)
\(\frac{{9x - 75}}{60} = \frac{569.2}{60}\)
or 9x - 75 = 569.2
So, 9x = 644.2
x = 71.57

None of the answer choices match. Could you please check the answer options?

You are wrong in highlighted portion..
\(\frac{{4x + 5x - 75}}{60} = \frac{569.2}{60}\)

It will be 4x+5x-25

Even though answer does not correspond to the given options.
Possibly options are wrong/incomplete.
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What is the source of this question?
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chetan2u


You are wrong in highlighted portion..
\(\frac{{4x + 5x - 75}}{60} = \frac{569.2}{60}\)

It will be 4x+5x-25

You are absolutely right. My bad.
The answer after the correction is 9x - 25 = 569.2
Or 9x = 594.2
Or x = 66.02
Still does not match any of the choices.

Thanks for pointing it out. Will edit it in my original post
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What is the source of this question?

It was a speed test question from adda247.
It's too bad when our answer is right but it's given in the option. It makes us too much confusing and wastes our time in find the correct solution even though we are right.
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(X/15)+(X/12)-(5/12)=(569.2)/60


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Solving for X would yield around 70 , so it might be D


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WizakoBaskar
pv8172
The total time taken by a boat to travel \(x\) km downstream and \((x - 5)\) km upstream was 569.2 minutes. If the difference between the speed of the boat downstream and that in upstream is 3 kmph and the respective ratio between speed of boat in still water and speed of water current was (9 : 1), what is the value of x?

A) 63.8
B) 34.4
C) 29.4
D) 68.8
E) 62.5


Let the speed of the boat in still water be B km/hr
Let the speed of water current be S km/hr.

Downstream speed = B + S
Upstream speed = B - S

Given data 1: Difference between speed of boat downstream and that upstream = 3 km/hr
So, (B + S) - (B - S) = 3
Or 2S = 3 or S = 1.5 km/hr.

Given data 2: Ratio between speed of boat in still water and speed of water current was (9 : 1)
B : S = 9 : 1
If S = 1.5 km/hr, B = 9*1.5 = 13.5 km/hr

The boat travels x km downstream. i.e., the boat travels x km @ (13.5 + 1.5) = 15 km/hr
The boat travel (x - 5) km upstream. i.e., the boat travels (x - 5)km @ (13.5 - 1.5) = 12 km/hr

Given data 3: Total time taken = 569.2 minutes = \(\frac{569.2}{60}\) hours.

Total time taken = \(\frac{x}{15} + \frac{{x - 5}}{12} = \frac{569.2}{60}\)
\(\frac{{4x + 5x - 25}}{60} = \frac{569.2}{60}\)
\(\frac{{9x - 25}}{60} = \frac{569.2}{60}\)
or 9x - 25 = 569.2
So, 9x = 594.2
x = 66.02

None of the answer choices match. Could you please check the answer options?

Hi,
15 x 4 = 60
Therefore
it should be
5x + 4x - (5 * 4) = 5x + 4x - 20
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pv8172
CAMANISHPARMAR
What is the source of this question?

It was a speed test question from adda247.
It's too bad when our answer is right but it's given in the option. It makes us too much confusing and wastes our time in find the correct solution even though we are right.

This is not a GMAT like question and should be removed.
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CAMANISHPARMAR
pv8172
CAMANISHPARMAR
What is the source of this question?

It was a speed test question from adda247.
It's too bad when our answer is right but it's given in the option. It makes us too much confusing and wastes our time in find the correct solution even though we are right.

This is not a GMAT like question and should be removed.

I totally agree.
This just requires long calculations and no "smart work"

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