Answer:
Aaron's checking account pay interest last cycle at $300
Explanation:
Banks pay pay interest on a daily basis compounded 365 days a year.
Interest paid for the first half of the month = $400
Interest paid for the second half of the month = $200
Now, for finding the average balance :
We add both the interests paid for the first and the second month then divide their sum by 2

So, Aaron's checking account pay interest last cycle at $300