How long did the flood last? Bible Contradictions

This Bible contradiction is from the Skeptic's Annotated Bible.

Verses

And the flood was forty days upon the earth; and the waters increased, and bare up the ark, and it was lift up above the earth.

And the waters prevailed upon the earth an hundred and fifty days.

And the waters returned from off the earth continually: and after the end of the hundred and fifty days the waters were abated.