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1030 grains of Sand

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by faraz_jeddah » Fri Aug 09, 2013 1:15 am
If there are 1030 grains of sand on Playa de Sonrisa, how many of these grains of sand are submerged by the ocean at least once a day?

A - 40% of the grains of sand are submerged at least twice a day.
B - 55% of the grains of sand are not submerged exactly once a day.

I picked E [spoiler]as the question does not state that the maximum number of times graincs can be submerged is 2 (twice). So I assumed there is a probability that the grains can be submerged 3,4,5 etc. times
[/spoiler]

OA is C
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Source: — Data Sufficiency |
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by GMATGuruNY » Fri Aug 09, 2013 1:51 am
faraz_jeddah wrote:If there are 1030 grains of sand on Playa de Sonrisa, how many of these grains of sand are submerged by the ocean at least once a day?

A - 40% of the grains of sand are submerged at least twice a day.
B - 55% of the grains of sand are not submerged exactly once a day.
[/spoiler]

OA is C
Statements combined:
Statement 1: 40% are submerged at least twice a day -- in other words, twice a day or more.
Statement 2: Since 55% are NOT submerged exactly once a day, 45% ARE submerged exactly once a day.
Thus:
Total percentage submerged at least once a day = (percentage submerged exactly once a day) + (percentage submerged twice a day or more) = 45+40 = 85%.
With this information, we can calculate how many of the 1030 grains are submerged at least once a day.
SUFFICIENT.

The correct answer is C.
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by Matt@VeritasPrep » Fri Aug 09, 2013 10:48 am
I think I wrote this question!

Faraz, your logic is pretty good, but "at least twice" doesn't imply exactly twice, so those grains could be submerged 3, 4, 5, ..., ∞ times. You only need to find the number that have been submerged at least once, which is essentially "exactly once" + "at least twice". (Numerically speaking, (≥1) = (1) + (≥2).)
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by faraz_jeddah » Fri Aug 09, 2013 11:02 am
Good Question and even better explanation! :mrgreen:
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by tarik » Thu Aug 22, 2013 9:33 am
I chose B for this one.
I didn't read the question carefully.
Thanks to the experts for their explanations.
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