Most credit cards charge interest based on the average daily balance per billing cycle. In this case each balance within the billing cycle is weighted by the number of days it exists. Suppose your credit card has a 30 day billing cycle and the balances over these 30 days are given in the table below.

Days Transaction balance days

1-8 remaining balance $1800 8

9-15 $900 purchase $2700 7

16-18 $700 purchase $3400 3

19-30 $1100 payment $2300 12

(a) Calculate the average daily balance for these 30 days.

(b) What would have been your average daily balance if you paid $2000 on day 17 instead of $1100 on day 19?