Data Sufficiency

bigb62387 wrote:Can't be anything other than A, right?

(1) Average = Sum / N

Sum = $51 million
N = 100
SUFFICIENT

(2) 60% sold at $450,000, but we're told nothing about the remaining 40%. They could have been sold for $1 a piece or $1 million a piece, and we would end up with 2 very different averages.
INSUFFICIENT

Brent@GMATPrepNow wrote:

theCodeToGMAT wrote:In Greenville last July, what was the average (arithmetic mean) home sale price?

(1) In Greenville last July, there were 100 homes sold for a total of $51 million.

(2) In Greenville last July, condominiums accounted for 60% of the home sales, and the average condominium price was $450,000.

I'm not sure how the answer isn't A

My full solution . . .

Target question: What was the average home sale price last July?

Statement 1: In Greenville last July, there were 100 homes sold for a total of $51 million.
Average home sale price = (sum of all sales)/(# of sales)
= $51,000,000/100
= $510,000
Since we can answer the target question with certainty, statement 1 is SUFFICIENT

Statement 2: In Greenville last July, condominiums accounted for 60% of the home sales, and the average condominium price was $450,000.
There are several possible cases that satisfy this condition. Here are two:
Case a: There were 5 home sales last July. 3 condos sold for $450,000 each, and 2 houses sold for $10 billion each. In this case, the average sale price is over $4 billion
Case b: There were 5 home sales last July. 3 condos sold for $450,000 each, and 2 houses sold for $1 each. In this case, the average sale price is less than $200,000
Since we cannot answer the target question with certainty, statement 2 is NOT SUFFICIENT

Answer = A

What the source of this question?

Cheers,
Brent

Brent@GMATPrepNow wrote:

theCodeToGMAT wrote: Brent, even I was quite satisfied that the Answer cannot be other than [A]. However, the explanation is also satisfying, making me feel that I was wrong.
According to the explanation, the Question Stem is seeking the Average price of HOME SALE PRICE. And, the Statement 1 describes the Average price of 100 Homes. So, explanation concludes that since we are provided the details of only 100 homes, we cannot extrapolate to give details of all home.

Hmmmmmmmmmmmmmmmmmmmmmmmm.
So, "there were 100 homes sold" does not mean that 100 homes sold? It means that more than 100 homes were sold?
I'm quite certain that the GMAT would not use such ambiguous wording. For example, if a GMAT question states that "Joe owns 3 cars," this does not mean that Joe might own more than 3 cars.

What's the source of this question?

Cheers,
Brent