QCAA General Mathematics Loans, investments and annuities 2
15 sample questions with marking guides and sample answers
Five years ago, a retiree invested $100 000 in a compound interest account earning 3.8% p.a. compounding monthly. They now intend to use the balance of the account to begin a perpetuity that will return 4% p.a. compounding annually and pay them $6000 each year.
Provide advice to the retiree about whether their compound interest investment is large enough to finance the perpetuity.
Reveal Answer
Compound interest investment
The balance of the investment account is $120 888.66.
Perpetuity
The present value of the perpetuity needs to be $150 000.
The compound interest investment will not provide enough money to finance the perpetuity.
| Descriptor | Marks |
|---|---|
correctly substitutes into an appropriate rule for compound interest investment | 1 |
determines balance of investment account | 1 |
correctly substitutes into an appropriate rule for perpetuity | 1 |
determines present value of perpetuity | 1 |
determines if the compound interest investment is large enough to finance the perpetuity | 1 |
Rita opens a savings account with an initial deposit of $4000.
The account earns interest compounding weekly. After the interest is added each week, Rita deposits an additional $50 into the account.
Assume there are exactly 52 weeks in one year.
The annual interest rate, compounding weekly, that is required to achieve a balance of $14000 after three years is closest to
8.4%
14.2%
14.6%
17.2%
Reveal Answer
8.4%
Correct. Setting up the annuity equation or using a financial solver yields an annual rate of .
14.2%
Incorrect. An annual interest rate of would result in a final balance of approximately $15,800, which exceeds the target of $14,000.
14.6%
Incorrect. An annual interest rate of would result in a final balance of approximately $16,100, which is significantly higher than the target of $14,000.
17.2%
Incorrect. An annual interest rate of would result in a final balance of approximately $17,700, which is much higher than the target balance of $14,000.
Jo contributes $2500 per quarter to an annuity earning 3.6% p.a. compounding quarterly.
At the end of 4 years, Jo makes a one-off extra contribution of $10 000 and continues with the regular quarterly contributions.
Determine the value of the annuity at the end of 6 years, to the nearest dollar.
Reveal Answer
Value of regular contributions
Value of extra payment
Total value
| Descriptor | Marks |
|---|---|
correctly determines the and values | 1 |
substitutes into appropriate annuity rule | 1 |
substitutes into appropriate rule | 1 |
determines sum of two values | 1 |
determines total value, rounded to the nearest dollar | 1 |
A couple saved for their retirement by making the same monthly payments for 20 years into an account that earned 4.2% p.a. compounded monthly.
At the age of 65, the couple retired and used all their savings to purchase a perpetuity with an interest rate of 5.76% p.a. compounded monthly, paying $3600 each month.
How much did they save each month to prepare for their retirement?
Reveal Answer
Perpetuity — find the size of the savings
Use the total savings to find the size of the monthly payment
The monthly savings were $1999.29.
| Descriptor | Marks |
|---|---|
Correctly determines the value | 1 |
Correctly recalls the perpetuity rule | 1 |
Determines purchase price of perpetuity | 1 |
Correctly determines the and values | 1 |
Correctly selects the appropriate annuity rule | 1 |
Determines payment | 1 |
Shows logical organisation, communicating key steps | 1 |
The following recurrence relation models the value, , of a perpetuity after time periods.
The value of can be found by calculating
Reveal Answer
This represents the value of , not . It fails to divide by the initial value when solving the equation.
In a perpetuity, the balance remains constant over time, so . Substituting this into the recurrence relation gives , which algebraically solves to .
This incorrectly divides by the payment amount instead of the principal amount when solving for .
This expression is equivalent to , which does not correctly solve the perpetuity equation for .
This expression is mathematically incorrect and does not follow from solving the constant balance equation .
Donald invests $250000 into a perpetuity at an interest rate of 5% per annum.
Donald receives a payment at the end of each year.
When will the sum of all annual payments to Donald first exceed $250000?
at the end of year 13
at the end of year 17
at the end of year 21
at the end of year 25
Reveal Answer
at the end of year 13
Incorrect. The annual payment is . After 13 years, the sum of payments is , which is less than $250,000.
at the end of year 17
Incorrect. The annual payment is $12,500. After 17 years, the sum of payments is , which has not yet reached $250,000.
at the end of year 21
Correct. The annual payment is . After 20 years, the total received is exactly $250,000 (), so the sum first exceeds $250,000 at the end of year 21.
at the end of year 25
Incorrect. Although the sum of payments after 25 years () exceeds $250,000, year 25 is not the first time this occurs.
A perpetuity earns interest quarterly at 5.2% p.a. and pays $975 each quarter.
Determine the quarterly interest rate.
Reveal Answer
Quarterly interest rate,
| Descriptor | Marks |
|---|---|
correctly determines the quarterly interest rate | 1 |
Calculate the value of the perpetuity.
Reveal Answer
The value of the perpetuity is $75 000.
| Descriptor | Marks |
|---|---|
substitutes into appropriate rule | 1 |
calculates value of perpetuity | 1 |
An annuity with an initial zero balance has $500 deposited at the end of every month. The annuity earns 4.8% p.a. interest, compounding monthly. At the end of the fourth month, the balance is closest to
$2002
$2008
$2012
$2014
Reveal Answer
$2002
This option is incorrect because it significantly underestimates the interest earned. The total principal deposited is $2000, and the compound interest over four months amounts to approximately $12, not $2.
$2008
This option is incorrect. While it accounts for some interest, it is lower than the actual future value calculated using the monthly compounding rate of .
$2012
This is the correct answer. Using the monthly interest rate and the future value of an annuity formula , the balance is approximately $2012.03.
$2014
This option is incorrect as it overestimates the final balance. The correct calculation yields a value closer to $2012.
Tam deposits a fixed amount at the end of each month into an account paying 8.6% p.a. compounding monthly. From an initial zero balance, she accumulates $51 343.85 in four years.
A financial planner has advised Tam that she would have been at least $3000 better off if she had instead deposited half of the fixed amount at the end of each fortnight into an account paying 7.9% p.a. compounding fortnightly.
Evaluate the reasonableness of this advice.
Reveal Answer
Monthly amount
Fortnightly annuity balance
The advice that she would have been at least $3000 better off is reasonable as $3597.76 > $3000.
| Descriptor | Marks |
|---|---|
correctly substitutes parameters into the appropriate annuity rule | 1 |
correctly determines the monthly amount | 1 |
determines value of fortnightly annuity | 1 |
determines difference in annuity balances | 1 |
compares values to evaluate the reasonableness of the advice | 1 |
Andr0e invested $18 000 in an account for five years, with interest compounding monthly.
He adds an extra payment into the account each month immediately after the interest is calculated.
For the first two years, the balance of the account, in dollars, after months, , can be modelled by the recurrence relation
After two years, Andr0e decides he would like the account to reach a balance of $30 000 at the end of the five years.
He must increase the value of the monthly extra payment to achieve this.
The minimum value of the new payment for the last three years is closest to
$189.55
$195.45
$202.35
$246.55
Reveal Answer
$189.55
First, calculate the balance after 24 months: . Then, solve for the new payment () over the remaining 36 months: , yielding , making this the closest option.
$195.45
This option is incorrect and likely results from miscalculating the accumulated balance after the first two years or using an incorrect number of compounding periods for the second phase.
$202.35
This option is incorrect. A common mistake is calculating the future value of the principal and the annuity separately without compounding the intermediate balance correctly over the final three years.
$246.55
This option is incorrect and likely stems from using the original $18,000 principal instead of the accumulated two-year balance as the starting amount for the final three years.
Patrick has retired and invested his lump sum superannuation payout of $717 850 at a rate of 5.7% per annum compounded monthly. He begins the investment strategy from 1 January.
Patrick will receive $4500 at the end of each month for general living expenses and will also receive a further $4000 at the end of each year for an annual holiday.
Identify this type of investment account.
Reveal Answer
Annuity
| Descriptor | Marks |
|---|---|
states correct answer | 1 |
Determine the balance in the account at the end of the first year.
Reveal Answer
N = 12, I = 5.7, PV = , PMT = 4500, P/Y = 12, C/Y = 12
FV = 704 420.20
Balance at end of year 1 =
| Descriptor | Marks |
|---|---|
uses at least 4 correct values for N, I, PV, PMT, P/Y, C/Y | 1 |
uses all correct values for N, I, PV, PMT, P/Y, C/Y | 1 |
determines correct value for FV | 1 |
determines correct end of year balance | 1 |
Determine the balance in the account at the end of the second year.
Reveal Answer
N = 12, I = 5.7, PV = , PMT = 4500, P/Y = 12, C/Y = 12
FV = 685 970.53
Balance at end of year 2 =
| Descriptor | Marks |
|---|---|
uses correct value for PV | 1 |
determines correct FV | 1 |
determines correct end of year 2 balance | 1 |
When Patrick retired, he also considered the option of setting up a perpetuity with his superannuation payout still at 5.7% per annum compounded monthly. Calculate the quarterly payments Patrick would have received with this perpetuity in place.
Reveal Answer
N = 2 (can be any value), I = 5.7, PV = , FV = 717 850, P/Y = 4, C/Y = 12
Quarterly payments = $10 278.03
| Descriptor | Marks |
|---|---|
uses at least 4 correct values for N, I, PV, FV, P/Y, C/Y | 1 |
uses all correct values for N, I, PV, FV, P/Y, C/Y | 1 |
states correct quarterly payments | 1 |
A $50 000 perpetuity earning fortnightly interest at 4.94% p.a. provides a regular fortnightly payment.
Calculate the fortnightly payment.
Reveal Answer
Fortnightly payment =
| Descriptor | Marks |
|---|---|
correctly provides mathematical reasoning or working to support the answer | 1 |
calculates fortnightly payment | 1 |
Calculate the perpetuity's effective annual rate of interest as a percentage.
Reveal Answer
The effective annual rate of interest is 5.06% p.a.
| Descriptor | Marks |
|---|---|
correctly provides mathematical reasoning or working to support the answer | 1 |
calculates effective interest rate as a percentage | 1 |
Emi decides to invest a $300000 inheritance into an annuity.
Let be the balance of Emi's annuity after months.
A recurrence relation that can model the value of this balance from month to month is
Showing recursive calculations, determine the balance of the annuity after two months.
Round your answer to the nearest cent.
Reveal Answer
| Descriptor | Marks |
|---|---|
Shows recursive calculations and determines the correct balance after two months, rounded to the nearest cent ($297,477.40) | 1 |
For how many years will Emi receive the regular payment?
Reveal Answer
15 years
| Descriptor | Marks |
|---|---|
Correctly determines the number of years Emi will receive the regular payment (15) | 1 |
Calculate the annual compound interest rate for this annuity.
Reveal Answer
3.6%
| Descriptor | Marks |
|---|---|
Correctly calculates the annual compound interest rate (3.6%) | 1 |
If Emi wanted the annuity to act as a perpetuity, what monthly payment, in dollars, would she receive?
Reveal Answer
$900
| Descriptor | Marks |
|---|---|
Correctly determines the monthly payment for a perpetuity ($900) | 1 |
A retiring mathematics teacher donates $4000 to the school where she has worked for many years to pay for a prize to be awarded to a student at the school's annual prize-giving ceremony.
The school principal sets up an annuity with this money, receiving an interest rate of 0.3% compounded monthly and using $250 at the end of each year to purchase the prize.
The school principal is considering changing this investment to a perpetuity after ten years so there will always be money available to award this prize. The financial institution at that time will offer them an annual interest rate of 4.2% compounded monthly.
The school principal states that the new minimum value of the annual prize should be $130.
Calculate the nominal annual interest rate.
Reveal Answer
| Descriptor | Marks |
|---|---|
states correct rate | 1 |
Determine a recursive rule to model the balance of the annuity at the end of each year.
Reveal Answer
Effective annual rate of interest = 3.66% (CAS 2 d.p.)
| Descriptor | Marks |
|---|---|
determines effective annual rate of interest | 1 |
states correct rule | 1 |
Determine how much money will be left in the annuity after five years.
Reveal Answer
i.e. $3442.67
| Descriptor | Marks |
|---|---|
correctly determines the amount left after 5 years | 1 |
Determine the number of years the school will be able to award this prize using this annuity.
Reveal Answer
,
Therefore the school will be able to award the prize for 24 years.
| Descriptor | Marks |
|---|---|
correctly calculates and terms | 1 |
correctly concludes it is 24 years | 1 |
Show that the yearly perpetuity amount received by the school will be insufficient to purchase the annual prize.
Reveal Answer
Therefore yearly amount = $118.85
Therefore there is not enough money for the yearly prize (less than $130).
| Descriptor | Marks |
|---|---|
correctly determines value of annuity after 10 years | 1 |
sets up correct equation | 1 |
calculates correct yearly payment | 1 |
states correct conclusion about amount of money for the yearly prize | 1 |
Determine the largest number of years the school principal can maintain the annuity before changing to a perpetuity and receive enough to cover the annual prize of $130.
Reveal Answer
,
uses finance app
I = 4.2, PV = , N = any positive value, FV = 2918.78, P/Y = 1, C/Y = 12,
gives PMT = 124.98, i.e. $124.98, which is not enough
uses finance app
I = 4.2, PV = , N = any positive value, FV = 3056.89, P/Y = 1, C/Y = 12,
gives PMT = 130.89, i.e. $130.89, which is enough
Therefore the school principal can maintain the annuity for eight years.
| Descriptor | Marks |
|---|---|
correctly determines value of annuity after nine and eight years | 1 |
calculates correct yearly payments (PMT) | 1 |
states that eight years is the largest number of years the school principal can maintain the annuity | 1 |
Matt is saving up to purchase a new boat. He deposits $14 500 into a savings account which is compounded monthly. The account pays an annual interest rate of 4.8% and he also deposits $300 into the account at the end of each month.
After four years, Matt makes a one-off deposit of $2500 into the savings account. His goal is to have a total of $50 000 by the end of the fifth year.
Calculate the monthly interest rate.
Reveal Answer
4.8 ÷ 12 = 0.4%
| Descriptor | Marks |
|---|---|
calculates correct rate | 1 |
Determine a recursive rule to model the balance of the savings account at the end of each month.
Reveal Answer
| Descriptor | Marks |
|---|---|
states correct rule | 1 |
states correct initial value | 1 |
After how many months will the balance of Matt's account first exceed $20 000?
Reveal Answer
Therefore after 15 months
| Descriptor | Marks |
|---|---|
correctly calculates 14th and 15th terms | 1 |
correctly concludes it is 15 months | 1 |
Determine the equal monthly deposits during the fifth year he will need to make to reach this amount.
Reveal Answer
33 402.99 + 2500 = 35 902.99
N = 12, I = 4.8, PV = –35 902.99, FV = 50 000, P/Y = 12, C/Y = 12
PMT = –1005.52
Therefore, deposits of $1005.52 per month
| Descriptor | Marks |
|---|---|
correctly calculates balance after 4 years | 1 |
adds 2500 to balance after 4 years | 1 |
states correct PV | 1 |
correctly states the remaining parameters | 1 |
determines correct monthly deposit | 1 |
Matt purchases his new boat, which costs him $47 500. He decides to take the remaining money and re-invest it in one of the following high-interest savings accounts.
Option 1: 5.52% per annum, compounded six-monthly.
Option 2: 5.5% per annum, compounded quarterly.
Determine which option Matt should choose, by calculating the effective annual rates of interest.
Reveal Answer
Option 1:
Option 2:
Therefore option 2 is the better choice as it has a higher effective interest rate.
| Descriptor | Marks |
|---|---|
correctly calculates effective interest rate for option 1 | 1 |
correctly calculates effective interest rate for option 2 | 1 |
correctly states option 2 is the better choice | 1 |