Hi I need help with the question below, I need to use arithmetic sequences to solve the question! "Mandy's friend Hahn deposited $200 in a bank...

Hello!

Let's find the month interest rate then the year (simple) interest rate will be

There are full months elapsed till the end of June. The entire amount deposited is So the profit is

At the first month the profit was At the second, ($200 was deposited two times). Then and so on, up to (including). This is an arithmetic sequence, each term is $200 greater than the previous.

We want to find the sum of an arithmetic sequence with terms, whose first term is and the last is

The formula is 

here it is 

And this is the profit, it is equal to So It is the same as (monthly). Yearly it is

The answer: the annual rate of simple interest is 1.8%.