12. In 2013, there was a "special" sandal trading rule in the Winniebago County market: if you buy one pair of sandals, it is traded at the original price of 50 yuan; if you buy a second pair, it is traded at a 60% discount of the original price; if you buy a third pair, it is half price. It is known that Javier bought three pairs of sandals according to this trading rule. Then he saved ( ).
(A) $25 \%$
(B) $30 \%$
(C) $33 \%$
(D) $40 \%$
(E) $45 \%$
12. B.

From the problem, what we need to find is
$$
150-(50+50 \times 60 \%+50 \times 50 \%)=45 \text { (yuan). }
$$

Thus, the savings amount to $\frac{45}{150} \times 100 \%=30 \%$.