FE Industrial & Systems common mistakes
FE Industrial & Systems · Understand the traps and how to avoid them.
Computing a confidence interval or hypothesis test with the wrong standard error - using sigma instead of s/sqrt(n), or using the paired-test formula on two independent samples - and then reporting a decisive conclusion from it.
Formulas look similar across one-sample, two-sample, and paired cases, and candidates pattern-match on keywords ('two means') instead of checking whether the samples are paired or independent and whether sigma is known.
What to do instead
Before substituting numbers, write down three things on the scratch sheet: paired or independent, sigma known or estimated, and sample size. Then select the formula from that classification, not from the wording of the question.
Mixing up the interest factors - applying (P/F) where (P/A) is required, or treating a gradient as a uniform annual series - and thereby getting an answer that is off by a factor of several years' worth of cash flow.
The factor tables and formulas are memorized as symbols, and under time pressure candidates grab the factor whose name looks closest rather than drawing the cash-flow diagram first.
What to do instead
Always sketch the cash-flow diagram with arrows and periods before touching a factor. Then state the conversion in words ('converting an annual series to a present worth') and only afterwards write the symbol.
Choosing the alternative with the highest net present value when the alternatives have different lives, different initial capital requirements, or the question has an explicit budget constraint.
NPV-maximization is over-learned from introductory problems; incremental analysis, annual worth over a common study period, and capital rationing are separate procedures that candidates skip.
What to do instead
Run a three-question gate: equal lives? equal investment? budget-constrained? If any answer is no, switch to incremental rate-of-return analysis, annual worth, or a benefit-cost ranking accordingly, and show the incremental comparison explicitly.
Treating the NCEES model law and board rules as generic 'be honest' advice and answering ethics items by personal intuition rather than by the hierarchy of obligations the code specifies.
Candidates prepare for ethics by skimming the code once, so they miss that the code ranks public safety paramount and imposes specific affirmative duties (reporting, seal use, competence limits) that override loyalty to an employer or client.
What to do instead
Memorize the ordered canons and drill the specific duty rules - seal usage, competence boundaries, notification of a violation, conflicts of interest - and answer each item by asking which canonical obligation is being invoked, not which action feels most collegial.
Balancing a mixed-model assembly line by assigning tasks in the order they are listed rather than by longest-task-time or ranked-positional-weight, then declaring the line infeasible when the cycle time is achievable.
Line balancing is taught as 'fill the station until it overflows,' so candidates use a first-fit heuristic; they also forget to convert demand into a cycle time before starting.
What to do instead
Step one: compute cycle time from demand and available time. Step two: apply the largest-candidate rule or ranked positional weight and compute the resulting balance delay and theoretical minimum number of stations as a check.
Building an MRP record and forgetting to net out on-hand inventory and scheduled receipts, or applying the lot-sizing rule to gross requirements instead of net requirements.
The record has many columns and candidates compute the gross-requirements row and the projected-on-hand row independently, so the lot-sizing rule gets applied to the wrong row.
What to do instead
Work the record in the fixed column order - gross requirements, scheduled receipts, projected on-hand, net requirements, planned order receipts, planned order releases - and never compute a lot size until net requirements has been filled in for that period.
Computing a from-to chart distance by summing straight-line distances rather than rectilinear distances along aisle, or ignoring the flow-weighted objective when proposing a department layout.
Diagrams invite straight-line measurement, and candidates do not connect the layout objective to the load-times-distance product that the from-to chart is meant to minimize.
What to do instead
Convert the chart into a load-distance matrix explicitly (flow times rectilinear distance) and compare the score of the proposed layout against the existing one before concluding an improvement.
Applying a standard-time or allowance formula with the performance rating in the numerator when it belongs in the denominator, or adding allowances to normal time when the allowance is defined on total time.
Observed time, normal time, and standard time are all 'times' with no dimensional cue, so the placement of the rating factor and the allowance base are easily swapped.
What to do instead
Write the definition of each quantity with its units on the scratch sheet and check the direction: a fast worker (rating above 100) must increase the standard, and allowance-on-total-time problems require dividing by (1 minus allowance).
Reading a control chart by comparing each point to the control limits only, and failing to flag runs, trends, or points near the centerline that indicate non-random patterns.
Candidates memorize the three-sigma limits and treat any point inside the limits as 'in control,' overlooking the supplementary run rules that the exam tests.
What to do instead
After plotting, run a checklist of pattern tests - eight consecutive points on one side of the centerline, six in a row trending, two of three beyond two sigma - and state which rule is violated before answering.
Formulating a linear program with the objective and constraints transposed, or solving a transportation problem by inspection instead of checking degeneracy and the optimality condition.
Word problems hide the roles of coefficients, and the transportation/assignment algorithms require explicit checks (m+n-1 occupied cells, improvement index) that are skipped when the matrix looks small.
What to do instead
Define decision variables in one sentence with units before writing anything else, label each constraint as resource or requirement, and after any transportation solution verify the number of occupied cells equals rows plus columns minus one before testing optimality.
Guessing between the various systems-engineering lifecycle views and answering a V-model, spiral, or waterfall item by recency bias instead of by which lifecycle characteristic the stem actually describes.
The lifecycle models share vocabulary like 'iteration' and 'verification,' and candidates rely on a single memorized diagram rather than distinguishing risk-driven iteration from sequential baselining from decomposition-and-integration.
What to do instead
Build a short comparison table keyed on three attributes - iteration driver (risk, requirements churn, none), verification placement, and integration approach - and classify the stem on those attributes before choosing.