Data Sufficiency

HI jjjinapinch,

When dealing with DS questions, you can sometimes get to the correct answer without doing much (if any) 'math' - as long as you understand how the information that you're given relates to the specific question that is asked.

Here, we're asked if AT LEAST 60% of the students in Pat's class walk to school. This is a YES/NO question.

1) At least 60 percent of the female students in Pat's class walk to school.

This fact discuss the FEMALE students, but we have no idea what percent of MALE students walk to class.

IF NONE of the males walk to class, then it's possible that that would 'bring down' the average and the answer to the question would be NO.
IF ALL of the males walk to class, then this would 'bring up' the average (to something even higher than the current percent of females walking to class) and the answer to the question would be YES.
Fact 1 is INSUFFICIENT

2) The number of students in Pat's class who walk to school is twice the number of students who do not walk to school.

Fact 2 gives us a ratio of data...
(Number that walk to class):(Number that don't walk to class) = 2:1

This means that for every 3 students, 2 walk to class... 2/3 = 66 2/3%.
This is GREATER than 60%, so the answer to the question is ALWAYS YES.
Fact 2 is SUFFICIENT

Final Answer: B

GMAT assassins aren't born, they're made,
Rich

jjjinapinch wrote:Do at least 60 percent of the students in Pat's class walk to school?

(1) At least 60 percent of the female students in Pat's class walk to school.
(2) The number of students in Pat's class who walk to school is twice the number of students who do not walk to school.

Official Guide question
Answer: B

We have to find out whether the number of students who walk to school ≥ 60% of the total number of students

Statement 1: At least 60 percent of the female students in Pat's class walk to school.

Say there are 100 female and 100 male students

Case 1: Assume that all male students walk to school.

=> Percentage of students who walk to school = [(100 + 60) / 200]*100% = 80% > 60%. The asnwer is YES.

Case 2: Assume that no male students walk to school.

=> Percentage of students who walk to school = [(60) / 200]*100% = 30% < 60%. The asnwer is No.

No unique answer. insufficient.

Statement 2: The number of students in Pat's class who walk to school is twice the number of students who do not walk to school.

Say x number of students do not walk to school; thus, the number of students who walk to school = 2x

=> Percentage of students who walk to school = [(2x) / (2x+x)]*100% = 200/3% = 66.67% > 60%. The asnwer is Yes.

The correct answer: B

Hope this helps!

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jjjinapinch wrote:Do at least 60 percent of the students in Pat's class walk to school?
(1) At least 60 percent of the female students in Pat's class walk to school.
(2) The number of students in Pat's class who walk to school is twice the number of students who do not walk to school.

Official Guide question
Answer: B

We need to determine whether at least 60 percent of the students in Pat's class walk to school.

Statement One Alone:

At least 60 percent of the female students in Pat's class walk to school.

We do not know how many male and female students are in Pat's class, nor do we know the percentage of male students who walk to school. Thus, statement one is not sufficient to answer the question.

Statement Two Alone:

The number of students in Pat's class who walk to school is twice the number of students who do not walk to school.

If we let n = the number of students who do not walk to school, then the number of students who do walk to school is 2n. Furthermore, the total number of students can be represented by n + 2n = 3n. Thus, the percentage of students who walk to school is:

(2n)/(3n) x 100% = 2/3 x 100% = 66.7%

Statement two is sufficient to answer the question.

Answer: B