11. For consumers, a simple $n \%$ discount is more suitable than the following plans:
【Plan 1】Two consecutive $15 \%$ discounts;
【Plan 2】Three consecutive $10 \%$ discounts;
【Plan 3】A $25 \%$ discount followed by an additional $5 \%$ discount.
Then the smallest possible positive integer $n$ is ( ).
(A) 27
(B) 28
(C) 29
(D) 31
(E) 33
11. C.

Let the original price of the product be $x$ yuan. Then, the unit price after discount according to Plan 1 is
$$
(1-15 \%)^{2} x=0.7225 x \text {; }
$$

The unit price after discount according to Plan 2 is
$$
(1-10 \%)^{3} x=0.729 x \text {; }
$$

The unit price after discount according to Plan 3 is
$$
(1-25 \%) (1-5 \%) x=0.7125 x \text {. }
$$

According to the problem,
$$
(1-n \%) x \leqslant \min \{0.7225 x, 0.729 x, 0.7125 x\} \text {. }
$$

Thus, $n \geqslant \max \{27.75,27.1,28.75\}$.
Therefore, the minimum possible value of $n$ is 29.