The proverbial 40days

I have been challenged during Bible lesson discussions and if you have time answer me (why) Noah made the Ark in 40 days, the rains/storm lasted for 40days, the Israelites walked through the desert for 40 years, the tower of barbel was built in 40 days,
Jesus Christ fasted for 40days and  He accended to heaven after 40 days,  Easter is celebrated after 40 days. Even when people are deceased they stop mourning after 40 days,  also people say a thief has 40days,  even an infant is normally taken outside after 40 days,  people say life begins at 40. Why 40? If you are defeated please send to others we might get an answer. Thx