Trust This Certificate represents ownership of a “regular interest” in a “real estate mortgage investment conduit,” as those terms are defined in Sections 860G and 860D, respectively, of the Internal Revenue Code of 1986, as amended. The issue date of this Certificate is December 28, 2005. Unless this Certificate is presented by an authorized representative of The Depository Trust Company, a New York corporation (“DTC”), to the Trust or its agent for registration of transfer, exchange, or payment, and any Certificate issued is registered in the name of Cede & Co. or such other name as is requested by an authorized representative of DTC (and any payment is made to Cede & Co. or to such other entity as is requested by an authorized representative of DTC), ANY TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL inasmuch as the registered owner hereof, Cede & Co., has an interest herein. WMALT Series 2005-11 Portion of the Class X Notional Amount as of the Cut-Off Date Evidenced by this Certificate: $13,411,848.00 Class X Certificate Interest Rate: 5.750%, applied to the Class X Notional Amount Cut-Off Date: December 1, 2005 First Distribution Date: January 25, 2006 Last Scheduled Distribution Date: January 25, 2036 Class X Principal Balance as of the Cut-Off Date: $0.00 Class X Notional Amount as of the Cut-Off Date: $13,411,848.00 Cede & Co. Registered Owner Exhibit A CUSIP 93934F JF0 WASHINGTON MUTUAL MORTGAGE PASS-THROUGH CERTIFICATE Class P Evidencing a beneficial interest in a pool of assets consisting of beneficial interests in another pool of assets consisting of, among other things, conventional one- to four-family mortgage loans formed by WaMu ASSET ACCEPTANCE CORP.