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Retired Moderator B
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If there are 1030 grains of sand on Playa de Sonrisa, how many of thes  [#permalink]

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Difficulty:   75% (hard)

Question Stats: 51% (01:47) correct 49% (01:39) wrong based on 333 sessions

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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?

(1) 40% of the grains of sand are submerged at least twice a day.
(2) 55% of the grains of sand are not submerged exactly once a day.
Math Expert V
Joined: 02 Sep 2009
Posts: 60480
Re: If there are 1030 grains of sand on Playa de Sonrisa, how many of thes  [#permalink]

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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?

(1) 40% of the grains of sand are submerged at least twice a day --> 0.4*1030 grains are submerged twice or more. Not sufficient,

(2) 55% of the grains of sand are not submerged exactly once a day. This imply that the remaining 45%, so 0.45*1030 grains, ARE submerged exactly once a day. Not sufficient.

(1)+(2) We have that 45% are submerged exactly once and 40% are submerged twice or more. Therefore, 45% + 40% = 85% are submerged at least once (once ore more). Sufficient.

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Re: If there are 1030 grains of sand on Playa de Sonrisa, how many of thes  [#permalink]

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9
1
I think I´ve come up with an alternative approach that could help you "visualize" this problem better.

There are 1030 grains, of which can be divided into 3 groups:
a- Submerged 0 times a day
b- Submerged only 1 time a day
c- Submerged 2 or more times a day

Question Stem
- Equation Given: a + b + c = 1030
- Question asked: b + c = ?
In summary, you have 3 variables and 1 equation

Statement 1

c = (0.4)1030
Insufficient

Statement 2
a + c = (0.55)1030
Insufficient

When you combine statements 1 and 2 plus the information given in the question stem, you yield 3 variables and 3 equations and hence you can solve.
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Intern  Joined: 19 Aug 2015
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Re: If there are 1030 grains of sand on Playa de Sonrisa, how many of thes  [#permalink]

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I have a doubt here

The question asks ...at least once a day...

i.e. number of grains per day submerged >= 1

S1 says - 40% number of grains per day submerged >=2

Why can't we answer the question by S1 only because if a grain is submerged twice then it would have submerged once also.
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Re: If there are 1030 grains of sand on Playa de Sonrisa, how many of thes  [#permalink]

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shahrukh0603 wrote:
I have a doubt here

The question asks ...at least once a day...

i.e. number of grains per day submerged >= 1

S1 says - 40% number of grains per day submerged >=2

Why can't we answer the question by S1 only because if a grain is submerged twice then it would have submerged once also.

You are missing the percentage of grains that was submerged exactly once.
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Re: If there are 1030 grains of sand on Playa de Sonrisa, how many of thes  [#permalink]

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Bunuel

in S2
ARE submerged exactly once a day
hence it is not suff - as the question asks at-least once a day?
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Re: If there are 1030 grains of sand on Playa de Sonrisa, how many of thes  [#permalink]

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paidlukkha wrote:
Bunuel

in S2
ARE submerged exactly once a day
hence it is not suff - as the question asks at-least once a day?

Yes.

The question asks: how many of these grains of sand are submerged by the ocean at least once a day? Or how many of these grains of sand are submerged by the ocean more than or equal to once a day.
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Re: If there are 1030 grains of sand on Playa de Sonrisa, how many of thes  [#permalink]

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JusTLucK04 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?

(1) 40% of the grains of sand are submerged at least twice a day.
(2) 55% of the grains of sand are not submerged exactly once a day.

1) 40%=>2
60%<=1

All 60% could be 1, all 60% could be 0. Insuff.

2) 45%=1
55% not 1. The 55% could all be 2, or the 55% could all be 0. Insuff.

1) & 2)

40%=>2
60%<=1

And if 45%=1, then 15%=0.
45%+40%=85%.
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If there are 1030 grains of sand on Playa de Sonrisa, how many of thes  [#permalink]

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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?

1) 40% of the grains of sand are submerged at least twice a day.
2) 55% of the grains of sand are not submerged exactly once a day.

Math Expert V
Joined: 02 Sep 2009
Posts: 60480
Re: If there are 1030 grains of sand on Playa de Sonrisa, how many of thes  [#permalink]

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1
AbhinavBankhwal 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?

1) 40% of the grains of sand are submerged at least twice a day.
2) 55% of the grains of sand are not submerged exactly once a day.

Merging topics. Please refer to the discussion above.
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Re: If there are 1030 grains of sand on Playa de Sonrisa, how many of thes  [#permalink]

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Bunuel 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?

(1) 40% of the grains of sand are submerged at least twice a day --> 0.4*1030 grains are submerged twice or more. Not sufficient,

(2) 55% of the grains of sand are not submerged exactly once a day. This imply that the remaining 45%, so 0.45*1030 grains, ARE submerged exactly once a day. Not sufficient.

(1)+(2) We have that 45% are submerged exactly once and 40% are submerged twice or more. Therefore, 45% + 40% = 85% are submerged at least once (once ore more). Sufficient.

Brunnel, if the question asked , what percent of sand is not submerged at all. Then also the answer could be C right?

So

(1) gives me at least twice. So, >=2.

(2) gives me Not submerged exactly once a day: comprising of No submerge & >=2.

so, 0.55-0.4=0.15.

Is this a correct ?
Math Expert V
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Re: If there are 1030 grains of sand on Playa de Sonrisa, how many of thes  [#permalink]

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SOUMYAJIT_ wrote:
Bunuel 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?

(1) 40% of the grains of sand are submerged at least twice a day --> 0.4*1030 grains are submerged twice or more. Not sufficient,

(2) 55% of the grains of sand are not submerged exactly once a day. This imply that the remaining 45%, so 0.45*1030 grains, ARE submerged exactly once a day. Not sufficient.

(1)+(2) We have that 45% are submerged exactly once and 40% are submerged twice or more. Therefore, 45% + 40% = 85% are submerged at least once (once ore more). Sufficient.

Brunnel, if the question asked , what percent of sand is not submerged at all. Then also the answer could be C right?

So

(1) gives me at least twice. So, >=2.

(2) gives me Not submerged exactly once a day: comprising of No submerge & >=2.

so, 0.55-0.4=0.15.

Is this a correct ?

Yes. We got that 45% + 40% = 85% are submerged at least once (once ore more), thus 15% are not submerged at all.
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Re: If there are 1030 grains of sand on Playa de Sonrisa, how many of thes  [#permalink]

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A very good question but very confusing due to the language of the question.. once can think submerged as the sand is submerged and gone into the sea.. SO the question should have clarified that the sand which is submerged remains there and is liable to be submerged again ..
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Re: If there are 1030 grains of sand on Playa de Sonrisa, how many of thes  [#permalink]

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JusTLucK04 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?

(1) 40% of the grains of sand are submerged at least twice a day.
(2) 55% of the grains of sand are not submerged exactly once a day.

for this question we need to carry the information that two tides happen a day. I got stumped as I thought that the grains can submerge more than three times also.
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Re: If there are 1030 grains of sand on Playa de Sonrisa, how many of thes  [#permalink]

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JusTLucK04 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?

(1) 40% of the grains of sand are submerged at least twice a day.
(2) 55% of the grains of sand are not submerged exactly once a day.

Official solution

Solution: C

We can solve this problem with either of the following equations: (Once per day) + (Twice or more per day) OR (All) – (Zero per day).

Statement (1) tells us that 40% of the grains are submerged 2+ times per day, so 60% are submerged either zero times per day or once per day, but we can’t break those groups up any further; INSUFFICIENT.
Statement (2) tells us that 55% of the grains of sand are submerged either zero times per day or 2+ times per day, but we can’t break those groups up either; INSUFFICENT.

Together, 40% are 2+, 15% are 0, and 45% are 1 per day. Therefore a full 85% are submerged at least once per day, and the correct response is (C). Re: If there are 1030 grains of sand on Playa de Sonrisa, how many of thes   [#permalink] 10 Dec 2019, 22:18
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