A quality control inspection reveals that 15 out of 200 installed light fixtures are not functioning properly. What is the defect rate, and what action should be taken?
Correct Answer
A) 7.5% defect rate; investigate root cause and implement corrective action
Defect rate = 15/200 = 7.5%. This rate is typically unacceptable and requires investigation of the root cause (installation procedure, product defect, etc.) and implementation of corrective action to prevent recurrence.
Why This Is the Correct Answer
Option A correctly calculates the defect rate as 15/200 = 7.5% and prescribes the appropriate response. A 7.5% defect rate is significantly high in construction quality standards and requires immediate investigation to identify the root cause (faulty installation procedures, defective products, inadequate training, etc.) followed by corrective action to prevent future occurrences. This systematic approach ensures quality improvement and prevents costly rework.
Why the Other Options Are Wrong
Option B: 0.75% defect rate; document and monitor
This option contains a calculation error, showing 0.75% instead of 7.5%. The decimal was misplaced by one position. Additionally, a 7.5% defect rate is too high to simply document and monitor without taking corrective action. This passive approach would allow the problem to persist and potentially worsen.
Option C: 7.5% defect rate; acceptable, no action needed
While the defect rate calculation of 7.5% is correct, considering this rate acceptable with no action needed is inappropriate. Industry quality standards typically expect defect rates well below 7.5%. Accepting such a high failure rate without investigation could lead to customer dissatisfaction, warranty claims, and reputation damage.
Option D: 15% defect rate; replace all fixtures
This option incorrectly calculates the defect rate as 15% instead of 7.5% (15/200 = 0.075 = 7.5%). Additionally, replacing all 200 fixtures when only 15 are defective is an extreme overreaction that would be unnecessarily costly and wasteful. The appropriate response is targeted investigation and correction.
Memory Technique
Remember 'SIREN' for defect response: Stop work, Investigate root cause, Repair defects, Evaluate process, Never accept high rates. For calculations: defects ÷ total × 100 = percentage.
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