40 is a symbolic number in the Bible representing a time of trial. It's not necessarily an exact reckoning of time. The actual duration of these events were 40 plus or minus. The number was used to show that it was specifically a time of trial. Kittel writes that "it came to mean a thorough and complete period of struggle, deprivation or self-denial."

D.L. Moody writes that there are seven "40 days" in the Bible:

[list]1. 40 days of sin and its judgments. Gn. 7.4, 12, 17
2. 40 days of law and mercy. Ex. 24.18; 34.28
3. 40 days of faith and unbelief. Dt. 9.9; Num. 13.14
4. 40 days of human weakness and divine strength. 1 Ki. 19.1-8
5. 40 days of repentance and forgiveness. Jonah 3
6. 40 days of conflict and victory. Lk. 4.2
7. 40 days of redemption and glory. Acts 1.3.[/list]

Jesus was tempted by the devil in the wilderness and then fasted for 40 days and 40 nights. Moses was on the mountain for 40 days. During the flood of Noah, it rained fro 40 days and 40 nights.