use mathematical induction theory. When doing that use (1-0.9) as 0.1 it will make proving for n=p+1 easier.
Spoiler:
Each year in June approximately 10% of the trees die out and in December, the workers plant 100 new trees. At the end of December, the workers plant 100 new trees. At the end of December 2000 there are 1200 trees in the plantation.
By considering 2001 as the first year. Show that the number of living trees at the end of December in the nth year is given by
No. of living trees
No idea where the 1000 came about
For the
So the part should be obvious.
Let's show that:
Take out a thousand:
Take out a tenth:
Geometric Series Found!
Good luck!