If there are 1030 grains of sand on Playa de Sonrisa, how many of thes

Question

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.

Bunuel · Accepted Answer

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.

Answer: C.

minwoswoh · Answer

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.
Correct Answer = C

shahrukh0603 · Answer

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.

Bunuel · Answer

You are missing the percentage of grains that was submerged exactly once.

paidlukkha · Answer

Bunuel

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

Bunuel · Answer

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.

Cez005 · Answer

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%.

SOUMYAJIT_ · Answer

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 ?

Bunuel · Answer

Yes. We got that 45% + 40% = 85% are submerged at least once (once ore more), thus 15% are not submerged at all.

shashankism · Answer

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 ..

kanthaliya · Answer

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.

mangamma · Answer

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).

Basshead · Answer

One way to visualize this problem is to consider that we have 3 different pots:

1. 0
2. exactly one
3. 2 or greater

What is the combined percentage of pots 2 and 3?

Statement 1 tells us the third pot consists of 40%. We don't know how much is in pot 2; INSUFFICIENT.

Statement 2 tells us pots 1 and 3 consists of 55%. We can conclude pot 2 consists of 45%; we can't, however, determine the percentage of pot 3. INSUFFICIENT.

Combined, we can conclude that pot 3 consists of 40% and post 2 consists of 45% for a combined total of 85%. SUFFICIENT.

Answer is C.

rvgmat12 · Answer

Official Explanation:

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).

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If there are 1030 grains of sand on Playa de Sonrisa, how many of thes

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If there are 1030 grains of sand on Playa de Sonrisa, how many of thes

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