I add about 1/2 cup of baking soda to every load of laundry. We have pretty hard water. The baking soda softens it so that it is more effective at washing away the detergent. Been doing this for a couple of years and I have noticed that our towels don't lose absorbency like towels we've had in the past.
The average number of children each woman will have over the course of her lifetime is called the Fertility Rate In 2011, the overall global life expectancy for both men and women was
So now we would have to find out how many women are in that age group. According to [3], there are about 2 billion women world-wide in that age group. That would give you the answer of about 334 million. Note that this is only a very rough ballpark number, as we do not have exact information about the global average menstrual cycle length, the exact population numbers etc.