This Bible contradiction is from the Skeptic's Annotated Bible.
2 Kings 12:1 View context
In the seventh year of Jehu Jehoash began to reign; and forty years reigned he in Jerusalem. And his mother's name [was] Zibiah of Beer-sheba.
2 Kings 13:10 View context
In the thirty and seventh year of Joash king of Judah began Jehoash the son of Jehoahaz to reign over Israel in Samaria, [and reigned] sixteen years.