Year in, year out, candidates make the same old mistakes when answering questions on limiting factors – and especially those concerning make- versus-buy decisions. It’s time to stop the rot
Every time I mark the Performance Man- agement paper, I constantly find the same errors on certain topics in each sit- ting, so see many students failing to achieve the mark that their efforts deserve. As a result, I have written an article on lim-iting factors that I hope will help you to avoid the same mistakes in your P2 exam.
his we can see that direct material is obviously the single limiting factor.
A common error at the start would be to assume that both the supply of material and working hours are limiting factors, and to produce figures accord- ingly. This practice is both technically incorrect and extremely time-consuming.
Once the limiting factor has been determined, the exercise can follow its usual course. First, we estab- lish the unit contribution per product; then we
calculate the contribution per unit of limiting factor, ranking each product accordingly (see table 3). Then we allocate what resource is available in a production plan (see table 4). This will leave a short- fall of 2,500 – 1,440 = 1,060 units of product B.
Common errors at this point include ranking the products on their contributions per unit made, which is fundamentally wrong and devalues the rest of the answer. Some candidates forget, or don’t realise, that only the variable costs should be subtracted from the selling price to arrive at the contribution. Again, this is a basic error and produces an incorrect ranking. In real situations this would have disastrous conse- quences for a company, in that it wouldn’t maximise its profit if it were to rank the products wrongly.
Make-versus-buy decisions In the worked example we have assumed that the company would not be able to meet the full budgeted demand for all four products. But if the company had received definite orders for all the demand figures quoted, it would need to decide which products to make and which to purchase. It must meet the demand – otherwise, it would incur penalty charges and lose the goodwill of its customers. Let’s consider
a simple example to develop this point. Working time is the limiting factor in this case – only 32,000 direct labour hours are available – and we have been given the data shown in table 5 above.
An analysis of the table shows that if we bought a unit of Z it would release two hours of labour to use, but each of these would cost the company £6. If we bought product X it would also release two hours of direct labour per unit, but the cost would be only £4 per hour of direct labour. Similarly, we can see that Y would be cheaper than X to buy. So the prior- ity for making the components in-house will be Z first, followed by X and then Y. The company will achieve a lower level of contribution by buying the products rather than making them, but it is reducing the impact on its profits by taking this approach.
The final position is shown in table 6 and the final contribution relating to satisfying the total demand for products X, Y and Z is shown in table 7.
A common error on such questions is to rank the products incorrectly. The rule here is to minimise the extra variable costs of subcontracting per unit of scarce resource saved. In this case, it means minimis- ing the cost per direct labour hour saved.
Combining the two techniques In the past few years the P2 paper has included ques- tions that combine a limiting-factor situation with a make-versus-buy decision. Let’s consider a simple question that is not complicated by the requirement to identify which cost item is the limiting factor but does feature the need to fulfil a one-off contract. Beta Manufacturing is a company that produces three products – R, S and T – using different quantities of the same resources. Information about the three products is shown in table 8.
Beta buys in a special component XX from a sup- plier called Gamma that it uses in making product T at £35 per unit. It is considering manufacturing this component in-house and has established that the total cost per unit of doing so would be as follows: direct material at 3kg per unit (£12) + direct labour (£8) + variable overhead (£6) = £26. The material used to produce component XX is the same material A that’s used in making products R, S and T. The quantity of output for component XX will relate directly to that of product T. Beta has also established that it can obtain only 57,000kg of direct material A per week for the foreseeable future.
You are required to:
1. Calculate whether the company should continue to purchase component XX from Gamma or whether it should manufacture this internally.
2. Prepare a statement to show the optimum weekly output based on your decision for requirement 1.
3. Explain any non-financial factors that Beta should consider before it decides whether or not to make component XX itself.
An analysis of table 9 shows that if the company manufactures component XX internally it will con- sume 3kg of direct material A per unit and each unit of XX will generate £3 per kg of this limiting factor. This figure is lower than those earned by any of Beta’s three existing products. Therefore, since com- ponent XX has the lowest rank, the company should continue to buy in XX so that the resources available can be used to manufacture products R, S and T. The resulting production plan (see table 10) indicates that Beta’s optimum weekly output would be 4,200 units of T, 1,800 units of R and 2,520 units of S.
We now need to calculate the purchase price of component XX at which Beta would manufacture it internally as opposed to buying it. This type of situation has featured in several recent P2 papers. The decision concerning the purchase of component XX would change if the contribution earned from manufacturing it equalled that of the lowest- contributing product of the other three. In this case it’s product S, which has a contribution of £4.80 per kg of direct material A. This is £1.80 higher than that from component XX. Because each unit of XX requires 3kg of direct material A, the buying price would have to be 3 x £1.80 = £5.40 per unit higher than it is at present. It would then have the same contribution per unit of limiting factor, and rank- ing, as product S. So the purchase price of XX at which Beta’s decision could change is £35 + £5.40 = £40.40 per unit.
If such a situation did actually arise and raw mate- rials were still in short supply, this would obviously open the door to another set of questions relating to the manufacture and supply of product S. I’ll discuss these points in the last part of the answer.
Common errors here include failing to realise that component XX is comparable with products R, S and T in arriving at a decision and, again, ranking a product on its contribution rather than on its con- tribution per unit of limiting factor.
The most relevant non-financial factors associated with this scenario are as follows:
Does Beta’s workforce possess the requisite skills to produce component XX?
Would Beta be able to manufacture component XX to the same standard as that achieved by Gamma – ie, would quality be compromised?
Does Beta have sufficient resources to manufac- ture component XX? Is special machinery needed, for example?
If Beta manufactures component XX internally, more of product S would have to be sacrificed. How might this affect the sales of products R and T?
How would Gamma react to losing its business with Delta? Could it jeopardise the relationship?
A typical error at this point would be to cite non- financial factors that do not relate to the scenario. I hope that this article has clarified any misun- derstandings associated with questions on limiting factors and make-versus-buy decisions. My advice to P2 candidates would be to:
Review the past papers and practise answering questions relating to this topic.
When attempting these questions, you should make every effort to lay out your answers clearly and also apply proper exam technique by completing them in the time allowed.
Visit CIMA’s website and read the post-exam guide relating to the past few sittings. This will give details of all common mistakes to avoid.