Solution:
Starting balance of Marlene for first 10 days of her 30 days billing cycle
= $ 570
Purchase made = $ 120
Total Balance after purchase made = $ 570 + $ 120 = $ 690
Payment made = $ 250
Balance for last 10 days = $ 690 - $ 250 = $ 440
Credit Card APR = 15% Annually
Credit Card APR = [tex]\frac{15}{12}=\frac{5}{4}[/tex] = 1.25% monthly
Amount charged as an interest for billing cycle = 440 [tex]\times \frac{1.25}{100}[/tex]
= [tex]\frac{550}{100}[/tex]
= $ 5.50 ( Amount charged)