Now ratsLevel pending
Note: a rat is counted as a pair of rats, definitely a male and a female. The rats (Asian house rats) may not give birth as quickly as the rabbits just now but they give birth to more. But lets make it a bit easier...
After being born, the rats are able to reproduce after three months.
From then on, they reproduce every two months. They give birth to 1 ( in reality, 6, but lets make it easier.) rats every time they reproduce.
They never die.
How many rats do we have at the end of a year?