Logical Thinking & Problem Solving Flashcards

A maintenance technician follows this decision rule: 'Replace a component only if ALL three conditions are true: vibration exceeds 0.8 in/s, temperature exceeds 180°F, AND runtime exceeds 5,000 hours.' A motor reads 0.9 in/s vibration, 175°F, and 6,200 hours. What is the correct action?

Answer: Do not replace — not all conditions are met

The rule requires ALL three conditions to be true simultaneously. Temperature is 175°F, which does NOT exceed the 180°F threshold. Since one condition fails, the conjunction is false and replacement is not warranted — even though the other two conditions are met.

A plant has four pumps: W, X, Y, and Z. The logic controller starts the standby pump whenever the running pump's output drops below 60 PSI. Pump W drops to 55 PSI, so X starts. X then drops to 58 PSI. Pump Y starts. Y maintains 65 PSI. Which pumps are running at the end of this sequence?

Answer: W, X, and Y

The logic starts a standby pump when output drops below 60 PSI, but there is no rule that stops the original pump. W dropped to 55 PSI (X started), X dropped to 58 PSI (Y started), Y holds at 65 PSI. None of W or X were shut down by the described logic, so all three — W, X, and Y — remain running.

A fault matrix shows: Fault A causes symptoms 1 and 3. Fault B causes symptoms 2 and 3. Fault C causes symptoms 1 and 2. A machine presents symptoms 1, 2, and 3 simultaneously. Which conclusion is best supported?

Answer: At least two faults are present, and multiple combinations are possible

Symptom set {1,2,3} can be explained by A+B (covers 1,3 and 2,3), A+C (covers 1,3 and 1,2), B+C (covers 2,3 and 1,2), or A+B+C. No single fault covers all three symptoms, so at least two faults must be present — but the data alone cannot uniquely identify which combination is occurring.

Five switches (1–5) control a conveyor segment. The conveyor runs ONLY when an odd number of these switches are ON. Currently switches 1, 2, and 4 are ON (conveyor running). A technician must turn ON switch 5 for a safety interlock test. What is the minimum additional change needed to keep the conveyor running?

Answer: Turn OFF any one of switches 1, 2, or 4

Currently 3 switches are ON (odd → conveyor runs). Turning ON switch 5 brings the total to 4 (even → conveyor stops). To restore an odd count while keeping switch 5 ON, the technician must turn OFF exactly one of the currently ON switches (1, 2, or 4), returning the total to 3.

A troubleshooting flowchart has this structure: Step 1 — Check fuse (blown → replace and TEST; good → go to Step 2). Step 2 — Check voltage at terminal (absent → go to Step 4; present → go to Step 3). Step 3 — Check motor winding resistance (high → replace motor; normal → go to Step 5). Step 5 — Replace control board. A technician finds: fuse good, voltage present, winding resistance normal. Which component does the chart direct him to replace?

Answer: The control board

Tracing the logic: fuse good → Step 2; voltage present → Step 3; winding resistance normal → Step 5 → Replace control board. The flowchart systematically eliminates the fuse, upstream wiring, and motor, leaving the control board as the directed replacement.

A batch process runs four sequential operations: Mix (8 min), Heat (12 min), Cool (10 min), and Fill (5 min). A second identical line can begin its Mix step only after the first line finishes Heating. If Line 1 starts at 0:00, what is the earliest time Line 2 can complete its Fill step?

Answer: 0:55

Line 1 finishes Heating at 0:00 + 8 (Mix) + 12 (Heat) = 0:20. Line 2 can begin Mix at 0:20. Line 2 then runs: Mix ends 0:28, Heat ends 0:40, Cool ends 0:50, Fill ends 0:55. Therefore, the earliest completion for Line 2's Fill step is 0:55.