Did it take a certain ship less than 3 hours to travel 9 kilometers?

MANHATTAN GMAT OFFICIAL SOLUTION:

Notice that the statements provide rates in meters per minute. A good first step here is to figure out how fast the ship would have to travel to cover 9 kilometers in 3 hours. Create an RTD chart, and convert kilometers to meters and hours to minutes:

180r= 9,000
r= 50

The question asks whether the ship traveled 9 kilometers in less than 3 hours. The ship must travel faster than 50 meters/min to make it in less than 3 hours. Therefore, the question is really asking, is r > 50?

(1): SUFFICIENT: If the average speed of the ship was greater than 55 meters per minute, then r > 55. Thus, r is definitely greater than 50.

(2): INSUFFICIENT: If the average speed of the ship was less than 60 meters per minute, then r < 60. This is not enough information to guarantee that r > 50.

Answer: A.


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Question : Did it take a certain ship less than 3 hours to travel 9 kilometers?
Speed = Distance / Time = 9/3 = 3 km per hour

Question REDEFINED: Is the Speed of certain Ship less than 3 km per hour?

Statement 1: The ship's average speed over the 9 kilometers was greater than 55 meters per minute.

i.e Average Speed of Ship > 55 meters per min
i.e. Average Speed of Ship > (55/1000) / (1/60)
i.e. Average Speed of Ship > 55*60 / 1000 Km per hour
i.e. Average Speed of Ship > 3.3 Km per Hour

hence, SUFFICIENT

Statement 2: The ship's average speed over the 9 kilometers was less than 60 meters per minute.

i.e Average Speed of Ship < 60 meters per min
i.e. Average Speed of Ship < (60/1000) / (1/60)
i.e. Average Speed of Ship < 60*60 / 1000 Km per hour
i.e. Average Speed of Ship < 3.6 Km per Hour

i.e. Average speed could be greater than or less than 3 km per hour

hence, NOT SUFFICIENT

Answer: Option

1) stat 1 tells us that the avg speed was >55 m per min..
so in 3 hours it would travel>55*3*60 or 9900...
so the ship took less than 3 hrs to travel 9 kms... suff

2) stat 2 tells us that the avg speed was <60 m per min..
so in 3 hours it would travel<60*3*60 or 10800...
so the ship could have travelled <>=9 kms... insuff

ans A
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Rephrasing the question in terms of speed since the options A and B are given in average speed.

Traveling 9 KMs in less than 3 hours means speed should be greater than (s=d/t) s> 9/3 or 3 KM/Hour or 3000 Meters/60 Mins or
50 meters/mins . So, we can rephrase the question as Is average speed is greater than 50 Meters/Min ?

(A) Sufficient

(B) Insufficient. Speed can be 10 meters/min, 50 meters/min or 59 meters/min (All are less than 60 meters/min)

Answer: A

Formula : Dist = Speed * Time
If Dist is constant & Speed Increases -> Time will decrease
If Dist is constant & Speed Decreases -> Time will Increase

Using statement 1: Speed Min ~ 55m/min, Dist = 9000m
Time Max = Dist/Speed Min = 9000/55 = 163mins < 3 Hrs [If speed > 55, time will decrease further]
Therefore sufficient!

Using statement 2: Speed Max ~ 60m/min, Dist = 9000m
Time Min = Dist/Speed Max = 9000/60 = 150mins [If speed decreases, time will increase further & may even exceed 3 hrs ]
Therefore Insufficient!

Hence A !!

Hi All,

A similarly-themed question can be found in the Diagnostic Test of the OG13/GMAT2015/GMAT2016:

if-paula-drove-the-distance-from-her-home-to-her-college-at-135196.html

GMAT assassins aren't born, they're made,
Rich

Speed = Distance / Time
And Avg Speed = Total Distance/Total Time
St 1 - Avg speed = more than 55meter/min = 55/1000 x 1/60(min) = 3.3km/h
9/3.3 < 3 for sure
Suff
St 2 - Avg speed = less than 60meter/min = lets say 20/1000x1/60 = 1.2km/h
9/1.2 > 3
also lets take Avg speed = 59meter/min = 9 / (59/1000 x 1/60) < 3

Thus NS

Answer A

Hi Bunuel -

if rate > 50 kms/hour (chosen randomly) and time < 2 hours (randomly)

will distance be >100 kms or will distance < 100 kms ?

When the signs are direction ally opposite - what are the rules for the multiplication

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