Jean is going on a one year expedition to study the population growth of a gaggle of Canadian geese. There are 1,000 geese in the gaggle at the beginning of the first year. The gaggle grows each year with the following characteristics:
a. There is an equal number of male and female geese that form couples.
b. The couples raise one gosling every spring.
c. At the end of each year, 20% of the geese die of natural causes.
d. One-year-old geese raise goslings as well.
Develop a formula to calculate the number of geese after 7 years. Write your answer and show your work.