Bunuel
In a class of 30 students, Emma secured the third rank among the girls, while her brother Ben studying in the same class secured the sixth rank in the whole class. Between the two, who had a better overall rank?
(1) Ben was among the top 25% of the boys merit list in the class in which 60% were boys.
(2) There were three boys among the top five rank holders, and three girls among the top ten rank holders.
This is a good example of a DS question where it's helpful to make deductions from the prompt and restate the question in a simpler form before moving on to the statements.The prompt gives us two different pieces of data: Emma is
third among girls, while Ben is
sixth overall. The question asks whether Emma or Ben had a better overall rank. It isn't clear how
third among girls fits with the question about overall rank.
What would it mean for Emma to have a better overall rank? At least 3 girls would have to perform better than Ben; that is, at least 3 girls would be in the top 5. If two or fewer girls are in the top five, the best Emma can do is 7th. So the question can be restated as:
Were 3 or more girls in the top 5?Statement 1:The class of 30 is 60% boys --> (0.60)30 = 18 boys
25% of 18 --> (1/4)18 = 4.5
To be within the top 25%, Ben must be in the top 4 boys.
Test the extremes:
If Ben is 1st among boys, then all 5 top slots are taken by girls (and Emma is among them), an answer of YES to our restated question.
If Ben is 4th among boys, then 3 of the top 5 slots are taken by boys and the remaining 2 slots are taken by girls (meaning Emma is worse than 6th) -- an answer of NO.
With a YES and a NO, the statement is
Insufficient.Statement 2:With 3 boys in the top 5, the remaining 2 slots are taken by girls (meaning Emma is worse than 6th) -- an answer of NO. This is a definite NO; there is no way to get an answer of YES.
Sufficient.
The answer is B.Note that you could also have restated the question as, "Were 2 or fewer girls in the top 5?" Then Statement 2 would be a definite YES instead of a definite NO. But in Data Sufficiency, a definite YES or a definite NO are equally good for sufficiency.
It's often helpful to spend some time working with the prompt, making deductions and possibly restating the question, before diving into the statements. The extra time up front can save you from having to do redundant work when working with the two statements.