Finance charge is equal to:
daily balance*A*P*R*billing cycle/365
db 0.1204 30/365 = 5.71
db = 577.01 (I am rounding every answer, and keeping the number in my calculator, things won't work out exactly if you calculate using my numbers)Manipulate the formula for mean:
average = total/amount
577.01 = total/30
total over 30 days = 17,310.22Set up an equation with our information:
606.40x + 55.25(30-x) = 17,310.22
551.15x = 16,652.72
x = 28.4
The balance was $606.40 for 28 days, so she paid on the 29th.