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Why does it say his 23rd year? Yo'ash became king in Yehu's seventh year, and Yehu ruled in all 28 years. If so, he died in Yo'ash's 21st year!
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Radak: We must say that Yo'ash became king at the beginning of Yehu's seventh year, and Yehoachaz became king at the beginning of Yo'ash's 23rd year. Malbim - i.e. it was after 21 full years. 1
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I would have said that it was 22 years later. Yehu began his 29th year, but did not complete it, so it is not counted for him. (PF)
