23-Ind-A2 Analysis and Design of Work · December 2013
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams — December 2013 — 98-Ind-A2 Analysis and Design of Work. Three-hour, closed-book exam (approved Casio/Sharp calculator only); any five of the seven questions constitute a complete paper and only the first five answered in the answer book are marked — all seven are solved below for completeness. The source prints Question 3's second and third sub-parts both labelled “(iii)” (a typesetting slip); they are answered here in the marking-scheme order (i)/(ii)/(iii), 8/6/6 marks.
Reference texts: Niebel & Freivalds, Niebel’s Methods, Standards, and Work Design (13th ed.) — operations analysis, workplace/tool design and motion economy, stopwatch time study, performance rating and allowances, predetermined time systems (MTM/MOST), work sampling, wage-incentive and job-evaluation systems.
Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.
This is a multiple-machine (interference) assignment problem of the type charted in Question 1(ii): the operator services each machine (loads/unloads/adjusts) for a fixed time, then the machine runs automatically while the operator moves on to the next machine.
Given.
| Quantity | Symbol | Value |
|---|---|---|
| Operator rate | $R_o$ | $12.00/hr |
| Machine rate | $R_m$ | $20.00/hr |
| Average machine downtime | $d$ | 6 min per 60 min scheduled |
| Servicing (load/unload) time per unit | $l$ | 12 min |
| Machine running time per unit | $m$ | 45 min |
| Machines assigned | $n$ | 4 |
Find. The expected unit cost of output for the four-machine assignment.
Approach. Inflate the machine running time for downtime, find the theoretical break-even number of machines $n'=(l+m_{eff})/l$, confirm the assigned $n=4$ machines fall on the operator-limited side of that break-even point, then price one full cycle (operator + all four machines) and divide by the units the cycle produces.
| Quantity | Value |
|---|---|
| Effective machine time, $m_{eff}$ | 49.5 min |
| Break-even machine count, $n'$ | 5.125 (operator-limited at $n=4$) |
| Cycle time, $T_c$ | 61.5 min (4 units/cycle) |
| Operator idle time per cycle | 13.5 min (machine idle = 0) |
| Cost per cycle | $94.30 |
| Expected unit cost | $23.575/unit |
A stopwatch records only the OBSERVED time of whichever operator happens to be on the job at the moment of the study, at whatever pace that individual actually worked — a mixture of true task content and the observed operator’s personal speed, skill, effort and any watch-consciousness distortion. Performance rating is the mechanism that removes the operator-specific component: the analyst judges the observed pace against an internalized concept of “100% normal” (a standard, sustainable, well-trained pace) and multiplies the observed time by that rating to obtain a normal time that is, in principle, independent of which individual was timed. Without rating, a standard set from a fast operator would be unachievable by an average worker, and one set from a slow operator would pay a premium for ordinary performance — either error destroys the fairness and the incentive value of the standard.
Allowances matter for a complementary reason: even a perfectly rated normal time describes only the pure work content of the cycle, with the operator working continuously at a sustainable pace and nothing else happening. In reality operators need personal time (washroom, water), experience unavoidable delays (waiting on material, minor equipment stoppages) beyond their control, and accumulate fatigue that a sustainable pace cannot fully absorb over a full shift. Allowances add a percentage for each of these categories so the resulting standard time is one a worker can meet, shift after shift, without being either impossibly rushed or systematically over-paid — exactly the personal/fatigue/delay allowances applied in Question 4(i). Rating and allowances are therefore the two corrections that turn a raw stopwatch reading, tied to one person on one day, into a defensible, repeatable standard.
Because performance rating is a subjective judgement, industry has developed several complementary approaches to control and reduce its error rather than eliminate the judgement entirely: (1) rating training and certification — analysts practice on rating films of known, independently verified paces (often via a rating clinic/synthetic-film program) until their individual ratings converge within a tight tolerance of the accepted value, and are periodically re-certified; (2) group/consensus rating — averaging the independent ratings of two or more trained analysts on the same observation reduces the effect of any one analyst’s bias; (3) predetermined motion-time systems (MTM, MOST — Question 5) bypass subjective rating altogether by assigning a fixed time to each basic motion from motion-picture studies of many experienced operators, so the resulting normal time carries no analyst-to-analyst variation; (4) statistical control of rating consistency — plotting an analyst’s ratings over time (or against a reference standard) on a control chart to detect drift toward looseness before it contaminates new standards; and (5) for allowances specifically, replacing a single blanket percentage with empirically measured allowances from work sampling (Question 6), which observes actual personal/delay/fatigue time directly across many random instants rather than assuming a fixed traditional percentage.
