In a retail store, the average (arithmetic mean) sale for month M was

You are right. With the mean and no of days, you can count total sales.

Total sales = mean * no of days

However, in both cases, we have only total sales given. There's no way to find mean without no of days. So, both are together insufficient. Hence (E)

I highlighted the portion that I do not agree with.

Total sales = average sale * number of sales, not number of days.

Question is asking for comparison between Average Sale of Month M and Month J.
Average sale = \(\frac{Total Revenue from All Sales}{No. of Sales}\)
Neither of the options gives the No. of sales, so Answer is E.

Hi rakaisraka,

Since the prompt focuses on the average SALE per month, we need to know the TOTAL revenue and the TOTAL number of sales (re: the total number of 'transactions'). The number of days in the month has NO impact on this question.

You'll notice that the nothing in the prompt ever describes the total number of transactions in either month M or month J, so there is no way to determine the average sale for either month (nor how those averages relate to one another).

Final Answer:

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

Average sale = total revenue/total no of sales.

Question asks about the average sale and the a) and b) gives the total revenue.

Since the denominator value is not given, we cannot calculate the average sale.

Hence E.

Solution:
Question is asking for the comparison between Average Sale of Month M and Month J.
Here the trap point is taking total sales as Total sales = mean * no of days
But the Average sale is given by \(\frac{(Total Revenue from All sales)}{(No of sales)}\)
To determine the average sale we need to know total revenue and number of sales.

Analysis of Statement 1: For month M, total revenue from sales was $3,500.
Here we know only about total revenue but no information about the number of sales.
Therefore the statement 1 is not sufficient. We can eliminate options A and D.

Analysis of Statement 2: For month J, total revenue from sales was $6,000.
Here also we know only about total revenue but no information about the number of sales.
Therefore the statement 2 is not sufficient.

Combining the statements 1 & 2; we get:
From statement 1: We know total revenue from sales was $3,500 for Month M.
From Statement 2: We know total revenue from sales was $6,000 for Month J
Still, we do not the number of sales, so we cannot answer the question.

So, the correct answer option is “E”.

Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.