Here's the algebraic solution.

Let x = the total sales for January
Let x = the total sales for February
Let x = the total sales for March
.
.
Let x = the total sales for August
Let x = the total sales for October
Let x = the total sales for November
Let x = the total sales for December

NOTE: We haven't yet assigned an expression for the total sales in September

Average monthly sales for the 11 months (excluding September) = (x+x+x+x+x+x+x+x+x+x+x)/11 = 11x/11 = x

Last September the sales total for a certain car dealership was 400% [b]greater than the average monthly sales total for the other 11 months. [/b]
Average monthly sales for the 11 months = x
The total sales for September = x + (400% of x) = x + 4x = 5x

The sales total for September was approximately what percent of the year´s sales?
TOTAL sales for the year = x+x+x+x+x+x+x+x+x+x+x + 5x = 16x
So, we need to convert 5x/16x into a PERCENT

5x/16x = 5/16, so one approach is to use long division to divide 16 into 5, and then convert that decimal to a percent.

Alternatively, we can use some estimation.
Take 5/16 and multiply a numerator and denominator by 6 we get the equivalent fraction 30/96
We know that 30/100 = 30%
Since the denominator, 96, is slightly less than 100, we know that 30/96 is slightly greater than 30%

Answer: C

Thank you so much brent!

Hello from the GRE Prep Club BumpBot!

Thanks to another GRE Prep 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.