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Homework Help: Calculating backlog in quarters

  1. Oct 28, 2014 #1
    Mod note: Moved from a technical math section, so the template doesn't appear.

    I have a demand for 6 quarters of [29, 24,32,21,31,21] and can produce 25 units each quarter.

    I am trying to calculate how many units I have to deliver at least 1 quarter too late and also how many units I deliver at least 2 quarters too late.

    Is my table correct ? I get so confused when I get to a production of <0.

    How can i calculate the ones that are at least one quarter too late and at least 2 quarters too late?

    Code (Text):
    Demand    Production    Backlog
        29          25             4
        24          21             3
        32          18             14
        21          4              17
        31          -13            44
        21          -57            78
    Last edited by a moderator: Oct 28, 2014
  2. jcsd
  3. Oct 28, 2014 #2


    Staff: Mentor

    In the first quarter, what happens to the backlog of 4? Does it get added to the demand for the next quarter? If it does, your table doesn't show it.

    How can production be negative? You can produce 15 things or 0 things, but what does it mean to produce -13 things?
  4. Oct 28, 2014 #3


    Staff: Mentor

    Is this a homework problem?
  5. Oct 28, 2014 #4

    Ray Vickson

    User Avatar
    Science Advisor
    Homework Helper

    I cannot figure out what you are attempting to do; your problem description makes no sense to me.

    Basically, you have a total 6-quarter demand of 29 + 24 + ... + 21 = 158, and a maximum possible 6-month production of 6*25 = 150. Therefore, no matter what you do you will have a total backlog of 158 - 150 = 8, and it will be even higher if you produce less than 25 in any quarters. Then, exactly what happens to the backlogs depends on the backlog-filling policy. For example, if you fill as much of previous backlogs as soon as possible, you can produce 25 in each of quarters 1,2, using 4 units of the Q2 production to fill the 4 units backlogged from Q1; that will leave 21 units available to meet Q2 demand, so you will end Q2 with a backlog of 24 - 21 = 3 units, etc.

    There are, of course, other policies possible, but since you do not specify any objective (such as minimization of some type of penalty cost), it is impossible to narrow it down to a single policy. You need to specify more information.
    Last edited: Oct 28, 2014
  6. Oct 28, 2014 #5


    Staff: Mentor

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