Grade 11 Mathematics
Grade 11 ¡ Term 2Mathematics

Finance, Growth & Decay

We extend Grade 10 finance to include nominal and effective interest rates, annuities and future value, and present value calculations.

Week 5

6.1 Nominal & Effective Interest Rates, Future Value

  • Convert between nominal and effective annual rates
  • Calculate the future value of periodic payments (annuities)
  • Solve for present value and time period
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Real-World Connection

A bank advertising '12% p.a. compounded monthly' is NOT the same as '12% per year'. The effective rate is higher because of monthly compounding. Understanding this difference prevents expensive surprises when comparing financial products.

Effective Annual Rate from Nominal

ieff=(1+inomm)m−1i_{\text{eff}} = \left(1+\frac{i_{\text{nom}}}{m}\right)^m - 1

$m$ = number of compounding periods per year; $i_{\text{nom}}$ = nominal annual rate

Future Value of Annuity

F=x⋅(1+i)n−1iF = x\cdot\frac{(1+i)^n - 1}{i}

$x$ = regular payment, $i$ = interest rate per period, $n$ = number of payments

Present Value of Annuity

P=x⋅1−(1+i)−niP = x\cdot\frac{1-(1+i)^{-n}}{i}

The amount needed NOW to fund $n$ future payments of $x$

â„šī¸ Note

For monthly payments at annual rate ii: use imonthly=i12i_{\text{monthly}}=\frac{i}{12} and n=12×yearsn=12\times\text{years}. Always match the frequency of the rate to the frequency of payments.

Worked Examples

Worked Example

Effective vs Nominal Rate

Problem

Find the effective annual rate for a nominal rate of 18% p.a. compounded monthly.

Worked Example

Future Value of Annuity

Problem

R500 is invested monthly for 5 years at 9% p.a. compounded monthly. Find the future value.
Activity — 8 Questions

CAPS Cognitive Level Distribution

L1 ¡ Knowledge2 Q
L2 ¡ Routine Procedures2 Q
L3 ¡ Complex Procedures2 Q
L4 ¡ Problem Solving2 Q
1
L1 ¡ Knowledge1 mark
Find the monthly rate if the annual rate is 12%.
2
L1 ¡ Knowledge2 marks
State the formula for effective annual rate from nominal rate compounded mm times.
3
L2 ¡ Routine Procedures3 marks
Find the effective annual rate for 24% p.a. compounded quarterly.
4
L2 ¡ Routine Procedures3 marks
R1 000 is saved monthly for 3 years at 6% p.a. compounded monthly. Find the future value.
5
L3 ¡ Complex Procedures4 marks
How much must be saved monthly for 10 years at 8% p.a. (monthly compounding) to accumulate R200 000?
6
L3 ¡ Complex Procedures5 marks
A loan of R80 000 is repaid over 5 years at 12% p.a. compounded monthly. Find the monthly payment.
7
L4 ¡ Problem Solving5 marks
Compare: investing R100 000 at 15% p.a. (simple) for 3 years vs 14% p.a. (compounded monthly) for 3 years. Which is better?
8
L4 ¡ Problem Solving6 marks
R500 000 is invested now at 10% p.a. compounded monthly. Monthly withdrawals of R6 000 begin immediately. How long before the account is empty?
Finance, Growth & Decay Grade 11 Maths CAPS Notes & Examples | MathSciBuddy