Answer:
50 %
Explanation:
A woman has fixed number of eggs. With each menstrual cycle, one egg is released. By the time a woman reaches the age of early 40s, the egg count has reduced tremendously and the chances of a woman being fertile are very low.
Along with women, men also develop some issues with their sperm count and speed.
Thus the probability of a man and woman having baby is 50% at the age of 40.