Sure Rich! I will be happy to show you how I worked through the question:

(1) The average speed at which Carlos cycles from his house to the library yesterday was greater than 16 feet per second.

For me is not sufficient because at this rate Carlos could have been cycled a distance less or greater than 6 miles.
Thas this fact is insufficient is quite evident, so I will focus no statement 2.

(2) The average speed at which Carlos cycles from his house to the library yesterday was less than 18 feet per second.

If the speed at which Carlos cycled was less than 18 feet per second, to check if the statement is sufficient, I can take in consideration a speed less than 18 feet/sec., for example 17 feet per second.
So, if Carlos cycled at 17 feet per second, it measn that his rate was also 1020 feet per minute and 30600 feet per 1/2 hour. Dividing 30600 by 5280 (1 mile = 5280 ft) I get 5,79 mile, which is not 6 mile. So, IMO Carlos didn't covered a distance greater or equal than 6 miles and the answer to the question is always NO.

Hope my line of reasoning was understandable, so you can quickly spot my mistake.

Thanks a lot

Couple of points to mention here. For saying statement 1 is not sufficient, you do not mention anything about the critical value of speed that will give you 31680 feet in 30 minutes. Without mentioning this value, how do you know whether 16 ft/s is sufficient ? What if 16 ft/s WAS the limiting value to give you 6 miles of distance travelled?

Coming back to your analysis of statement 2, when you have speed < 18 ft/s, you have infinite possible values to check and nowhere in the question was it mentioned that the limiting speed is an integer value. So, assuming speed = 17 ONLY had no basis. The limiting value is actually 17.6 ft/s which is still <18 . This is where you made a mistake.

DS questions are specially tricky if you do not follow step by step procedure and should never assume things not given.


Hope this helps.
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Thanks a lot! now it is clear.

One more question: is this an hard question? I mean, is this question skippable or it counts?

Hi pepo,

It looks like you knew how to handle the calculations and overall logic just fine. The little mistake you made was in calculating the distance traveled at 17 feet/second and not 18 feet/second. Fact 2 gives us an 'upper limit' based on 18 feet/second, so THAT is the distance that we want to figure out. Anything LESS than THAT distance is possible.

Ultimately, while the work involved in this question was a bit 'thicker' than a typical prompt, the work itself was not 'hard work' (it was unit conversions and some arithmetic) - thus, I would NOT call this a hard question. On Test Day, you have to be responsible for the 'gettable' questions, regardless of how they might be 'ranked.' If you can nail those questions, then you'll end up with an upper-level GMAT score.

GMAT assassins aren't born, they're made,
Rich
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Attached is a visual that should help.

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Attached is a visual that should help.

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Hi Bunuel - is there a compilation of certain conversions that the GMAT may expect us to know? For example, I have never used miles per hour so I did not know the conversion.

You are not supposed to know that 1 mile = 5280 ft but should be able to convert miles per hour to feet to hour given that 1 mile = 5280 ft. That's why it's given that 1 mile = 5280 ft.

Generally, the question itself will supply the relative conversions, so 1m = 100cm or 1km = 1,000m will be given. Though you should have a few basic ones memorized: 1 hour = 60 minutes, ...

Check other Conversion problems to practice in Special Questions Directory.
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Answer: Option E

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If it took Carlos 1/2 hour to cycle from his house to the library yesterday, was the distance that he cycled greater than 6 miles? (Note: 1 mile = 5280 ft)

Distance = Speed * Time
here we need to check whether the distance covered is greater than 6 miles or not
is Distance > 6 miles ?
Speed * time > 6 miles ?
Speed * 1/2 > 6 ?
Speed > 12 miles/hour ?
Since the unit of speed in the statements are given in feet/sec , we need to convert miles/hour to feet/sec
1 miles/hour = 5280/(60*60) feet/sec = 44/30 feet/sec
12 mile/hour = 12* 44/30 = 17.6 feet/sec
So we can re-frame the question stem as whether the speed is greater than 17.6 feet/sec or not.

(1) The average speed at which Carlos cycles from his house to the library yesterday was greater than 16 feet per second.
Statement 1 is insufficient as we cannot confirm that Speed > 17.6 or not

(2) The average speed at which Carlos cycles from his house to the library yesterday was less than 18 feet per second.
Statement 2 is also insufficient as we cannot confirm that Speed > 17.6 or not

Even though if we combine Statement 1 and 2 , we can only say that 16 feet/sec < speed < 18 feet/sec.
This is not sufficient to answer our question whether the speed is greater than 17.6 feet/sec or not.
If speed is 17 feet/sec, then its a NO and if speed is 17.8 feet /sec then its a Yes
So both Yes and NO is possible as the answer for the question, hence insufficient

Option E is the answer

Thanks,
Clifin J Francis
GMAT SME
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