Anyone know how many Mantis are in an Egg Case?

This morning my wife called me to "identify" a bug she found in one of here
house plants. Turned out to be a very small baby Mantis. Closer inspection
found more, and eventually we found an egg base on a Sweet Potatoe vine she
had brought in for the winter. We spent the next hour or more catching
dozens of baby mantis and transplanting them to other house plants around
the house.