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Author:  questioner [ Thu Dec 09, 2010 8:06 pm ]
Post subject:  GMAT Data Analysis (Data Sufficiency)

The table above shows quantities of the mobile phone models sold by a retailer. If prices did not change between 2003 and 2004, was the company’s total revenue from sales of these models in 2004 greater than its total revenue from sales of these models in 2003?
(1) Model A was the most expensive phone.
(2) Model C was the least expensive phone.

A. Statement (1) BY ITSELF is sufficient to answer the question, but statement (2) by itself is not.
B. Statement (2) BY ITSELF is sufficient to answer the question, but statement (1) by itself is not.
C. Statements (1) and (2) TAKEN TOGETHER are sufficient to answer the question, even though NEITHER statement BY ITSELF is sufficient.
D. Either statement BY ITSELF is sufficient to answer the question.
E. Statements (1) and (2) TAKEN TOGETHER are NOT sufficient to answer the question, meaning that further information would be needed to answer the question.

(A) In 2004, the retailer sold 15 fewer Model A phones and 15 more phones that were either model B or C.

Statement (1) tells us that Model A is the most expensive. Since the selling prices remained unchanged, the loss of revenue from selling 15 fewer of the most expensive phone must be greater than the increase in revenue from selling 15 more of the cheaper phone. So revenue must have decreased, and Statement (1) is sufficient.

Statement (2) tells us only that Model C is the least expensive phone. Since the retailer sold more Model B phones and fewer Model A phones, we need to know more information. If Model B phones were much more expensive than Model A phones, revenue might have increased. If Model A phones were much more expensive, revenue might have decreased.

Since Statement (1) is sufficient and Statement (2) is insufficient, the correct answer is choice (A).
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How do we know that the price of model B and model C put together is not more that the price of model A alone?