Reducing-balance depreciation models
Use a fixed fraction of the current asset value, not a fixed dollar loss. State the initial value, time unit, precision and modelling assumptions
- Keep the remaining fraction For annual depreciation r%, subtract the rate fraction from 1. Here the rate is strictly between 0% and 100% \(\displaystyle R=1-\frac{r}{100}\)
- State the complete recurrence Use the purchase value at index 0 and multiply the current value at each yearly step \(\displaystyle \begin{gathered}V_0=P\\V_{n+1}=RV_n\end{gathered}\)
- Use repeated multiplication or a power After n completed years there have been n updates. Values and losses use the ideal unrounded model \(\displaystyle V_n=PR^n\)
- Distinguish value, one-year loss and total loss A loss is a positive decrease in asset value, not interest earned. Subtract full-precision values before rounding the result \(\displaystyle \begin{gathered}L_n=V_{n-1}-V_n\\L_{\mathrm{total}}=P-V_n\end{gathered}\)
- Compare like-for-like models Flat-rate depreciation removes the same dollar amount based on the purchase price each year. State the rate, horizon and any cent-rounding convention before comparing
- State the model limits A constant percentage is an assumption, not a guarantee of resale prices. Repairs, market changes, disposal and a salvage floor may require another model or a restricted time interval
Worked example
A business buys a forklift for $12,000. It depreciates at 20% of its current value each year. Construct the recurrence, find its value after three years and the loss during year 3 alone
- \(\displaystyle R=1-20/100=0.8\)The multiplier is the fraction remaining, not the fraction lost
- \(\displaystyle \begin{gathered}V_0=12000\\V_{n+1}=0.8V_n\end{gathered}\)V(n) measures dollars after n completed years. State a constant reducing-balance model with no additions or disposal over this three-year horizon
- \(\displaystyle \begin{gathered}V_2=12000(0.8)^2=7680\\V_3=12000(0.8)^3=6144\end{gathered}\)Use the unrounded model. Both values happen to be exact dollars here
- \(\displaystyle \begin{gathered}L_3=7680-6144=1536\\L_{\mathrm{total}}=12000-6144=5856\end{gathered}\)The year-3-only loss is $1,536. Total loss over three years is $5,856
Common mistakes
Difficulty levels
Questions about this topic
What is a complete recurrence?+
Give the purchase-time value and the forward update, for example V(0)=8000;V(n+1)=0.85*V(n). Use V and n, omit dollar signs, and include both equations for the one joint mark. Exact fraction multipliers are also accepted
Why does the dollar loss get smaller?+
The same positive percentage is applied to a smaller current value. The percentage rate stays fixed; the dollar amount lost does not
Is depreciation loss a kind of interest?+
No. It is a fall in an asset’s modelled value. Here one-period loss subtracts consecutive values, while total loss compares purchase and final values
Why can subtracting displayed cents give the wrong loss?+
The displayed values may each be rounded. Subtract the two unrounded model values first, then round the requested loss once
Why does the flat-rate comparison mention rounding?+
The retained comparison contract fixes an annual dollar loss rounded to cents once, then subtracts that same amount each year. A model using an unrounded fixed loss can differ by a few cents; follow the stated convention
Does an exact-table question prove the model will continue?+
No. The question states a constant reducing-balance model. Without that assumption, two values can be followed by many different future sequences
Can the value reach zero?+
With a positive initial value and a multiplier strictly between zero and one, no finite exact model value is zero. A rounded display can show zero; real salvage value and disposal need separate consideration
Are my written models and explanations automatically marked?+
No. Construct your own response before viewing a model, then compare or ask a teacher to review it. Automatic numerical or full-rule entries do not certify an investigation or a written justification
Can I use a calculator?+
A calculator is allowed unless a question is marked no calculator
Which year level and chapter is this?+
Year 11, VCE Units 1 & 2, General Mathematics, chapter 3: Sequences and finance