# Question #de9db

##### 1 Answer

Jan 1, 2018

Total interst is

#### Explanation:

To begin with, let's see how much the company will pay in the first two months.

[First month]

Interest:

Principal:

Total:

[Second month]

Interest:

Principal:

Total:

How about the last month?

[Last(18th) month]

Interest:

Principal:

Total:

Then, what is the sum of the interest?

**arithmetic progression**.

The sum of an arithmetic progression is

Substitute

Thus, the total interst the company has to pay is