Housecat Reproduction

[Hornbein]

Start with one hundred housecats. Given unlimited resources, in seven years you will have a billion housecats.

 

[pinball1970]

Start with one hundred housecats. Given unlimited resources, in seven years you will have a billion housecats.

Are they all female?

 

[pinball1970]

Start Jan 1st. For one female cat they can have 20 kittens in a year, average 4 litters and 5 kittens per litter.
Kitten can reach puberty at 4 months so they start contributing by August, 25 kittens between them.
There must be a geometric series that can do this easier than brute forcing it.