Question

A pair of newborn male and female rabbits is placed in an enclosure to breed. The rabbits start to bear young one month after their own birth. At the end of each month, they have another male-female pair, which in turn mature and start to bear young one month later. None of the rabbits die. How many pairs of rabbits will there be at the end of six months from the start?

Answer 1

now, end of 0 months :2
at the end of 1 month :4
at the end of 2 months = 8 or 2^3
...
at the end of 6 months = 2^5 = 32 rabbits, or 16 pairs