Med books all say smthng different re sperm lifespan.1 book says max is 4 dys, 1 book says max is 5 dys, 1 bk says max is 6 days, another book says max is 7 days. which book is correct? very confused!

It's all the same: In real life, in one woman, nobody knows exactly when all the sperm are dead, when the egg actually pops out of an ovary, when an egg is fertilized, nor when a fertilized egg implants into the uterus... All dates are estimates, so 4 days = 5 days = 6 days = 7 days. They are all the same day in real life. As long as the husband is the only source of sperm, none of this matters.