Data Sufficiency

On a certain item, a discount of x% on the marked price gives a trader a profit of 2x% on the cost price. Is his profit more than 40% of the cost price?

A. The marked price is more than 1.8 times the cost price
B. The marked price is more than 1.7 times the cost price

What's the best way to verify which statement is sufficient? Can any experts help?

ardz24 wrote:On a certain item, a discount of x% on the marked price gives a trader a profit of 2x% on the cost price. Is his profit more than 40% of the cost price?

A. The marked price is more than 1.8 times the cost price
B. The marked price is more than 1.7 times the cost price

Let C = $100 and M = marked price.

Test the THRESHOLD:
2x% profit = 40%, implying that the x% discount = 20%.
Resulting values:
Discounted selling price = C + (2x% profit) = 100 + (40/100)(100) = 100+40 = 140.
Since the $140 discounted selling price constitutes a 20% discount off the marked price, $140 is equal to 80% of the marked price:
140 = (80/100)M
140 = (4/5)M
700= 4M
M = $175.

The values in blue imply the following:
When M=175, the 2x% profit = 40%.
Thus:
For the 2x% profit to be GREATER THAN 40%, M > 175.
Question stem, rephrased:
If C=100, is M > 175?

Statement 1:
If C=100, then 1.8C = (1.8)(100) = 180.
Since M > 180, the answer to the question stem is YES.

Statement 2:
If C=100, then 1.7C = (1.7)(100) = 170.
In this case:
It is possible that M=171, with the result that the answer to the question stem is NO.
It is possible that M=180, with the result that the answer to the question stem is YES.
Since the answer is NO in the first case but YES in the second case, INSUFFICIENT.

The correct answer is A.