Hi candygal79,

This question can also be solved by TESTing THE ANSWERS.

One of those 5 answers, when increased by 35% will equal $670

Let's say that you started with answer D and did a rough estimate...

$574 x 10% = about $57
$574 x 30% = about $171
$574 + $171 = $745 which is TOO HIGH

Now let's try answer B and do a rough estimate...

$512 x 10% = about $51
$512 x 30% = about $153
$512 x 35% = about $178
$512 + $178 = $690 which is TOO HIGH

The final answer MUST be lower than answer B

Final Answer: A

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

I just wanted to point out that all students should know Rich's technique for finding x percent of y.
It's based on the fact that it's incredibly easy to find 10% of any value. For example, 10% of 39 is 3.9, and 10% of 4210 is 421.

Also notice that, if we can find 10% of a number, it's just as easy to find 5% of that same number.
For example, since 10% of 42 is 4.2, we know that 5% of 42 will be 2.1 (i.e., HALF of 4.2)
Likewise, since 10% of 680 is 68, we know that 5% of 680 will be 34 (i.e., HALF of 68)

So, to find 15% of x, we'll find 10% of x, and we'll find 5% of x
For example, let's find 15% of 180.
10% of 180 = 18
So, 5% of 180 = 9
This means that 15% of 180 = 18 + 9 = 27

Cheers,
Brent