There was an incessant torrential downpour for “forty days and forty nights”; “the waters continued overwhelming the earth” a hundred and fifty days. (Ge 7:4, 12, 24)
Five months after the downpour began, the ark “came to rest on the mountains of Ararat.” (Ge 8:4)
It was nearly two and a half months later before “the tops of the mountains appeared” (Ge 8:5), another three months before Noah removed the ark’s covering to see that the earth had practically drained (Ge 8:13), and nearly two months later when the door was opened and the survivors set foot on dry ground once again.—Ge 8:14-18.
Noah and his family entered the ark in the 600th year of Noah’s life, the 2nd month (October-November), the 17th day.
(Ge 7:11) One year later (a year consisting of 360 days) was the 17th day, 2nd month, 601st year. Ten days after that would be the 27th day of the 2nd month, when they came out.
This totaled of 370 days, or parts of 371 separate days, spent in the ark. (Ge 8:13, 14)
In the log that Noah kept, it appears he used months of 30 days each, 12 of them equaling 360 days. In this way he avoided all the complicated fractions involved had he used strictly lunar months consisting of slightly more than 29 1⁄2 days. That such calculations were used in the account is evident from the fact that a five-month period consisted of 150 days