What percentage of the current fourth graders at Liberation Elementary

Question

What percentage of the current fourth graders at Liberation Elementary School dressed in costume for Halloween for the past two years in a row (both this year and last year)?

(1) 60% of the current fourth graders at Liberation Elementary School dressed in costume for Halloween this year.
(2) Of the current fourth graders at Liberation Elementary School who did not dress in costume for Halloween this year, 80% did not dress in costume last year.

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gmatophobia · Answer

We can use a 2*2 matrix to approach this question

Last Year - Dressed in Costume   Last Year - Not Dressed in Costume   Total  
  This Year - Dressed in Costume  x      
  This Year - Not Dressed in Costume        
  Total      t  
 
We have to find the value of  \frac{x}{t}

Statement 1

(1) 60% of the current fourth graders at Liberation Elementary School dressed in costume for Halloween this year.

Last Year - Dressed in Costume   Last Year - Not Dressed in Costume   Total  
  This Year - Dressed in Costume  x    0.6t  
  This Year - Not Dressed in Costume      0.4t  
  Total      t

We don't have sufficient information to answer the question. Hence, we can eliminate A and D.

Statement 2

(2) Of the current fourth graders at Liberation Elementary School who did not dress in costume for Halloween this year, 80% did not dress in costume last year.

Last Year - Dressed in Costume   Last Year - Not Dressed in Costume   Total  
  This Year - Dressed in Costume  x    t - m  
  This Year - Not Dressed in Costume  0.2m  0.8m  m  
  Total      t

We don't have sufficient information to answer the question. Hence, we can eliminate B.

Combined

Last Year - Dressed in Costume   Last Year - Not Dressed in Costume   Total  
  This Year - Dressed in Costume  x    0.6t  
  This Year - Not Dressed in Costume  0.08t  0.32t  0.4t  
  Total      t

However, the information is still not sufficient to find the value of  x  or  \frac{x}{t} .

The statements combined do not help.

Option E

mmdfl · Answer

1) what about LY? INSUFF
2) "Of the current fourth graders at Liberation Elementary School who did not dress in costume for Halloween this year..." How many? INSUFF
1 & 2) 
CY = Current Year
---------------------- | CY | LY
dress Halloween | 60% | 100%-z
not dress Halloween | 40% | z= 80%*40% + 60%*y%=32%+0.6y%

We want 60%*(100%-z). But z is undefined, because y is undefined
ANSWER: E

juliusskinner15 · Answer

how option 'E' is right, Can any one help me with it

What percentage of the current fourth graders at Liberation Elementary

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	Last Year - Dressed in Costume	Last Year - Not Dressed in Costume	Total
This Year - Dressed in Costume	x
This Year - Not Dressed in Costume
Total			t

GMAT Data Sufficiency (DS) Questions

What percentage of the current fourth graders at Liberation Elementary

Prep Toolkit

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

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My Rewards