Question

5. Each year a tree farm grows 40 more trees than the number of trees grown the previous year. The farm sells all of their trees each season (or year). If the farm started out with 30 trees in 2007, how many trees were sold in total up to and including the 2016 season?

Answer 1

1710 trees up to 2016 (not including 2016)

2100 trees up to 2016 (including 2016)

Explanation:

Given that

Farm started with 30 trees in 2007.

Every year 40 more trees than the previous year.

It is actually an Arithmetic Progression (AP) with

First term, a = 30 and

Common Difference, d = 40

The AP will look like:

30, 70, 110, 150, ....

We have to find the sum of this AP upto 9 terms and 10 terms:

9 terms sum will give us the total number of trees up to 2016 (not including 2016).

10 terms sum will give us the total number of trees up to 2016 (including 2016).

Formula for sum of 'n' terms of an AP:

`S_n=(n)/(2)(2a+(n-1)d)\\\Rightarrow S_9=(9)/(2)(2* 30+(9-1)40)\\\Rightarrow S_9=(9)/(2)(60+320)\\\Rightarrow S_9=(9)/(2)(380)\\\Rightarrow S_9=9 * 180 = 1710`

`S_(10)=(10)/(2)(2* 30+(10-1)40)\\\Rightarrow S_(10)=5(60+360)\\\Rightarrow S_(10)=5 * 420\\\Rightarrow S_(10)=2100`

1710 trees up to 2016 (not including 2016)

2100 trees up to 2016 (including 2016)