Final answer:
The people of Nineveh repented and turned from their evil ways when Jonah preached about their impending destruction.
Step-by-step explanation:
When Jonah preached, "Yet forty days, and Nineveh shall be overthrown!" the people of Nineveh repented and turned from their evil ways. They recognized the seriousness of Jonah's message and took it to heart. They fasted, put on sackcloth, and turned away from their wickedness, hoping that God would spare them from destruction. As a result of their repentance, God showed mercy to the people of Nineveh and spared them from their impending doom.