## To calculate November's interest using the average daily balance method, you need to determine the daily balance of Nancy's account for each day in November. Here's how you can do it using an Excel spreadsheet:

1. Open a new Excel spreadsheet and create a column for the dates of November (from November 1 to November 30).

2. In the column next to the dates, enter the respective account balances for each day. Start with the beginning balance of $600.

3. For each day, calculate the balance by adding any new purchases and subtracting any payments made that day. For example, on November 5, the balance would be $600 + $80 = $680.

4. Continue calculating the daily balances until you reach November 30.

Once you have the daily balances, calculate the average daily balance by summing up all the daily balances and dividing by 30:

Average Daily Balance = (Sum of Daily Balances) / 30

Next, multiply the average daily balance by the APR interest rate divided by 12 to get the monthly interest:

Monthly Interest = (Average Daily Balance) * (APR / 12)

Since the spilled paint obscured the specific interest charges on the statement, we need to use the average daily balance method to calculate the interest. With the given information, you can compute November's interest using the above steps in Excel.

Now, let's calculate the interest Nancy would have paid with the previous balance method and the adjusted balance method:

a) Previous Balance Method:

Under the previous balance method, the interest is calculated based on the balance at the end of the last billing cycle (in this case, October's ending balance of $600). Multiply this balance by the APR interest rate divided by 12:

Interest with Previous Balance Method = $600 * (APR / 12)

b) Adjusted Balance Method:

Under the adjusted balance method, the interest is calculated based on the outstanding balance after adjusting for any payments made during the current billing cycle. In this case, the outstanding balance after the $200 payment on November 10 would be:

Outstanding balance = $600 (beginning balance) + $80 + $100 + $50 - $200 (payment) = $630

Multiply this adjusted balance by the APR interest rate divided by 12:

Interest with Adjusted Balance Method = $630 * (APR / 12)

To compare the two methods, you can simply compute both interests using the above formulas.

As for choosing a credit source when opening the account, assuming Nancy would increase her outstanding balance over time, the adjusted balance method would be more desirable. This is because the adjusted balance method takes into account payments made during the billing cycle, resulting in lower interest charges compared to the previous balance method, which only considers the balance at the end of the previous billing cycle.

Calculating interest and comparing different credit sources accurately requires detailed knowledge of the specific terms and conditions of each credit source. It's always recommended to review and compare the terms and conditions of different credit sources before making a decision.