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Limiting factors – Linear Programming

VIVA

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  1. thank you for the good lecture?, my questions are (i) are you always suppose to guess the contribution in order to get ISO cont line in the exam or sometimes its given to you? (ii)are you suppose to show all the steps involved..

    • Certainly on one occasion you were actually given the graph (with the iso-contribution line) and expected to then use it.
      Otherwise you will be expected to draw the line yourself and because the angle is all that matters you need to ‘guess’ any level of contribution in order to get the angle.

      Yes – I stress in the lecture that you do need to show the steps. In Section B of the exam the marks are for each bit of the workings – not simply for the final answer – and if you do not show any of the steps then you do not get the marks for them.

  2. hi
    i tried to plot the graph using S as x-axis and E as y-axis but graph is turning out to be weird and making no sense to me ?
    how do we decide what to take for x-axis and y-axis ?
    thanks in advance

  3. Hello sir , i was wondering when calculating both equation for maximum contribution , do i have to show the workings on how I arrive at S and E (using the example) ? are there marks provided for the calculation because there is a faster way to calculate them on the calculator . Thank you 馃檪

    • Although by all means calculate the figures themselves on your calculator, you must show working in the exam.
      It is the workings that get the marks (and even if you have made a mistake you will still get most of the marks if you were doing it the right way).

      (This only applies to section B of the exam. In Section A (the MCQ’s) any workings are for your benefit but they will not be looked at – all that gets marked is the final answer.)

    • You will be required to draw the graph (unless the graph is actually drawn for you in the question which happened on one occasion).

      It is impossible to know which equations to solve for the optimal mix without having the graph (and the iso-contribution line).

  5. Sir,
    Is it necessary to develop an equation in order to find out the values for point B? Because if the graph is drawn on the “graph paper”, It could easily be seen from the graph. Then why wasting time on these simultaneous equations?

  6. Hello dear sir , i have some question regarding linear programming.
    1 : While preparing graph , how to estimate about units at x-axis and y-axis i am confused about what limit to take on both side. ?
    2: Once we prepared our graph , how we can identify feasible region i mean how to identify A and then B and so on. ?
    Thanks

  7. Hi, Thanks for your great explanation of this. The only thing I’m not sure about or may have missed is, … How did you choose 180 as the maximum limitation for labour hours ? You said at the start you would come back to it, but I never caught it.

    Many thanks

  8. Hi Mr Moffat, it’s really great the way you explained this. You really make it easy to follow and understand.

    Not sure I heard why you chose 40 as the max number on the graph. Please advise. Thanks alot.

    • I went through each constraint and calculated what points I needed to plot before actually drawing the lines.
      So for materials I need S=0, E=20; and E=0, S = 40.

      I did the same for each constraint, and then made sure the axis went far enough to be able to post the biggest S and the biggest E.

  12. Hi Sir, in the exam if for example I do the E on the y-axis and S on x-axis obviously the graph will look different but the numbers will still be the same. Is that ok? if not how should I know which product should I put on the x/y axis?

    Thanks

  13. Hi John

    I’m stuck 馃檨

    1. When we find the slope of the ISO line, and push it out, we find the nearest ‘point’ (in this case it was B). This gives us the highest contribution point. Is this correct?

    2. When working out S/E, do we always find the intersect of material v labour line? Then work out C?

    Thank you in advance!

    • 1. We move out the contribution line to the furthest point away from the origin, without leaving the feasible region.

      2. When finding the optimal mix, we solve together the two lines that intersect at the point where the contribution is the highest (i.e. the point found in (1) above). It certainly will not always be where material and about lines intersect – it could be any two constraints depending on the question.

      • Thanks, got it!

        Although I understand, I find it very difficult to understand the 15 mark questions for this topic. In particular I struggle to recognise what the constraints are, and therefore I find it difficult to nail down a formula.

        Not expecting a response..I guess I’ll just keep practicing questions to get the hang of it!

        Awesome work that you guys are doing – me and my colleagues appreciate it a lot

      • You are correct – it is down to question practice. You must obviously learn the technique, but actually sorting out the constraints for each particular question is something you cannot really learn – every question is different – and you can only get good at by practicing.

        Thank you for your comment as well 馃檪

  14. Sir, i am a student of the Institute of Chartered Accountants of Nigerian (ICAN). I have been writing perfromance management and FR since 2012 when the syllabus was changed. Right now, they no longer test MCQ and SAQ which has made it difficult to score cheap marks. Please advice me as am almost fed up with the whole examination.

    • I am sorry, but I really don’t know the syllabus or anything for ICAN. All we have is the lectures etc for the ACCA exams. I am sure that some of them will be relevant for your exams, but I can’t really say any more given my lack of knowledge on ICAN.

      • Thank you sir. ICAN and ACCA use same syllabus except for Public Sector Accounting and Finance (PSAF), Advanced Taxation and Business Law.

        Anyway, i have really gained a lot from open tuition. I have this courage that am going to pass the next diet since my enrolment on this forum. Thank you once again

  16. Sir, instead of writing the algebra for number of units of S and E that produce maximum contribution, can I just pinpoint the number from point B since I know that is the point of maximum contribution? I got exactly S= 30 and E=5 from the graph that I drew.

  19. This is probably a silly question, I’m possibly missing something … but why do we need to do the graph? Why can we not just use the equations to determine the optimum solution?

    • No you can’t (and I do explain why not in the lecture).

      If there are three (or more) constraints, then solving the equations for 2 of them at a time will not tell you whether or not they are inside or outside the other constraints.

      In addition, the examiner specifically tests you on whether or not you understand the graph – sometimes you have been asked to draw the graph, and on other occasions you have been given the graph. In either case, simply solving equations would not be doing what was required.

      • Oh I see, thank you. And my apologies for asking something you answered in the lecture. So much information to try and retain!

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