Data Sufficiency

This is a question form GMATprep and I got it wrong.

I think answer is A.

Lets consider we have 3 items: I1, I2, I3.
I1 is expensive one and I3 is cheapest one among the list.

BY STATEMENT A

I1 = 50$, discount = 20%, effective price = 40$;
I2 = 20$, discount = 10%, effective price = 18$;
I3 = ?

The maximum value of I3 can be equal to I2 only.

therefore, if I3 = I2 = 20$, discount = 10%, effective price = 18$;

Net effective price = 40 + 18 + 18 = 76$

If user buy these items in a group and got 15% discount on overall.
Then price after 15% discount will be 76.5$

BY STATEMENT B

I1 = ?
I2 = ?
I3 = 15$

The minimum value of I1 and I2 can be only equal to I3.
So,

I1 = 15$, discount = 20%, effective price = 12$;
I2 = 15$, discount = 10%, effective price = 13.50$;
I3 = 15$, discount = 10%, effective price = 13.50$;

Net effective price = 12 + 13.50 + 13.50 = 39$

If user buy these items in a group and got 15% discount on overall.
Then price after 15% discount will be 38.50$

So, Statement is not alone sufficient to give the result, however statement A is alone sufficient to give the answer.

Please do let me know the correct answer, so that I can understand that my approach is correct or not.

PS: Why I consider maximum price for statement A and minimum price for Statement B? Read Maxima Minima. It will give you clear cut idea.

OA is A,
I made a silly mistake in calculations and though C