During a summer sale, a clothing store offers a special on T-shirts. If you buy one T-shirt at the regular price of $30, you get the second one at a 10% discount, the third one at a 30% discount, and the fourth one at a 50% discount. David bought four T-shirts using this special offer. What percentage of the total regular price did he save?
20%
22.5%
25%
27.5%
30%
