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Tina inherits $60,000 and invests it in an account earning interest at a rate of 0.5% per month - HSC - SSCE Mathematics Advanced - Question 26 - 2020 - Paper 1

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Question 26

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Tina inherits $60,000 and invests it in an account earning interest at a rate of 0.5% per month. Each month, immediately after the interest has been paid, Tina withd... show full transcript

Worked Solution & Example Answer:Tina inherits $60,000 and invests it in an account earning interest at a rate of 0.5% per month - HSC - SSCE Mathematics Advanced - Question 26 - 2020 - Paper 1

Step 1

a) Use the recurrence relation to find the amount of money in the account immediately after the third withdrawal.

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Answer

To find the amount in the account after three withdrawals, we will apply the recurrence relation step by step:

  1. Calculate A1A_1:
    A1=60,000imes(1.005)800A_1 = 60,000 imes (1.005) - 800
    =60,000imes1.005800=59,500= 60,000 imes 1.005 - 800 = 59,500

  2. Calculate A2A_2:
    A2=59,500imes(1.005)800A_2 = 59,500 imes (1.005) - 800
    =59,500imes1.005800=58,997.50= 59,500 imes 1.005 - 800 = 58,997.50

  3. Calculate A3A_3:
    A3=58,997.50imes(1.005)800A_3 = 58,997.50 imes (1.005) - 800
    =58,997.50imes1.005800=58,492.49= 58,997.50 imes 1.005 - 800 = 58,492.49

Thus, the amount of money in the account immediately after the third withdrawal is $58,492.49.

Step 2

b) Calculate the amount of interest earned in the first three months.

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Answer

To calculate the total interest earned in the first three months:

  1. Total withdrawals after 3 months: 800imes3=2400800 imes 3 = 2400

  2. Initial balance was $60,000, and the balance after three withdrawals is: 60,00058,492.49=1,507.5160,000 - 58,492.49 = 1,507.51

  3. Thus, the interest earned is: 24001,507.51=892.492400 - 1,507.51 = 892.49

So, the interest earned in the first three months is $892.49.

Step 3

c) Calculate the amount of money in the account immediately after the 94th withdrawal.

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Answer

To find the amount in the account after 94 withdrawals, we can derive a formula:

  1. The recurrence relation can be expressed as:
    A_n = 60,000(1.005)^n - 800 imes rac{(1.005^n - 1)}{0.005}
    This formula accounts for the interest accumulated and the total withdrawals.

  2. For n=94n = 94:
    A_{94} = 60,000(1.005)^{94} - 800 imes rac{(1.005^{94} - 1)}{0.005}
    Calculating this yields approximately:
    A94extisabout187.85A_{94} ext{ is about } 187.85.

Thus, the amount of money in the account immediately after the 94th withdrawal is approximately $187.85.

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