Jerry has a credit card that uses the average daily balance method. For the first 14 days of one of his billing cycles, his balance was $1050, and for the last 16 days of the billing cycle, his balance was $1280. If his credit card’s APR is 19%, which of these expressions could be used to calculate the amount Jerry was charged in interest for the billing cycle?

1 answer

To calculate the interest charge using the average daily balance method, we first need to determine the average daily balance for the entire billing cycle.

  1. Calculate total balances for each period:

    • For the first 14 days, Jerry's balance was $1050: \[ \text{Total for the first 14 days} = 1050 \times 14 = 14,700 \]
    • For the last 16 days, Jerry's balance was $1280: \[ \text{Total for the last 16 days} = 1280 \times 16 = 20,480 \]
  2. Add the totals together to get the total balance for the entire billing cycle: \[ \text{Total balance for the cycle} = 14,700 + 20,480 = 35,180 \]

  3. Calculate the average daily balance for the entire billing cycle:

    • The total number of days in the billing cycle is \(14 + 16 = 30\). \[ \text{Average daily balance} = \frac{35,180}{30} \approx 1,172.67 \]
  4. Determine the daily interest rate:

    • The APR is 19%, which is expressed as a decimal for calculations: \[ \text{Daily interest rate} = \frac{19%}{365} \approx \frac{0.19}{365} \approx 0.00052055 \]
  5. Calculate the interest charged for the billing cycle:

    • Multiply the average daily balance by the daily interest rate and then by the number of days in the billing cycle: \[ \text{Interest for the billing cycle} = \text{Average daily balance} \times \text{Daily interest rate} \times \text{Number of days} \] Plugging in the numbers: \[ \text{Interest} = 1,172.67 \times 0.00052055 \times 30 \]

Thus, any expression that models \( \frac{35,180}{30} \times \frac{0.19}{365} \times 30 \) can be used to calculate the amount Jerry was charged in interest for the billing cycle.

Another way to express the interest can be simplified as: \[ \text{Interest} = \frac{35,180 \times 0.19}{365} \]

These would be valid representations of the interest charged for Jerry's billing cycle.