Question

Each year a tree grows 5cm less than it did in the preceding year.if it grew by 100cm in the first year in how many years will it have creased growing ?

Answer 1

HERE IS YOUR ANSWER, FRIEND.

The situation can be depicted as an AP.
here,
a = 100
d = -5
n = number of years before it stops growing.
then,
n-th term of this AP IS 0., i.e.,
$a_{n} = 0 \\ \implies a + (n - 1)d = 0 \\ \implies 100 + (n - 1)( - 5) = 0 \\ \implies \frac{100}{5} = (n - 1) \\ \implies \boxed{n = 21}$
So, before 21 years, the tree will have stopped growing.

HAPPY LEARNING.