Data Sufficiency

AAPL wrote:GMAT Prep

The attendees at a certain convention purchased a total of 15,000 books. How many of these attendees were female?

1. There was a total of 4,000 attendees at the convention.
2. The male attendees purchased an average (arithmetic mean) of 3 books each, and the female attendees purchased an average of 5 books each.

The OA is C.

Given: Few attendees at a certain convention purchased a total of 15,000 books.
Question: How many of these attendees were female?

Let's take each statement one by one.

1. There was a total of 4,000 attendees at the convention.

Certainly insufficient.

2. The male attendees purchased an average (arithmetic mean) of 3 books each, and the female attendees purchased an average of 5 books each.

Say the number of male attendees = x and the number of female attendees = y

=> 3x + 5y = 15,000

Many possible values of y. No unique answer. Insufficient.

(1) and (2) together

From Statement 1, we have x + y = 4000
From Statement 2, we have 3x + 5y = 15,000

=> y = 1,500. Sufficient.

The correct answer: C

Hope this helps!

-Jay
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