Lean Six Sigma Green Belt Certification Core Lean Principles 4 — Questions and Answers
Question 1: What is Mura in Lean, and how does it differ from Muda?
- Mura is waste; Muda is overburden
- Mura is unevenness or variability in flow; Muda is waste that adds no value (Correct answer)
- Mura is a defect type; Muda is a process step
- Mura and Muda are interchangeable terms for the same concept
Correct answer: Mura is unevenness or variability in flow; Muda is waste that adds no value
Mura describes unevenness or inconsistency in workflow (e.g., feast-and-famine production cycles), while Muda refers specifically to non-value-adding activities.
Question 2: A Lean team uses a heijunka box to schedule work. What problem is heijunka designed to solve?
- Overproduction driven by push scheduling
- Unevenness (Mura) in production by leveling type and volume (Correct answer)
- Excess inventory by reducing batch sizes to zero
- Waiting waste by speeding up the slowest process step
Correct answer: Unevenness (Mura) in production by leveling type and volume
Heijunka (production leveling) smooths production volume and mix over time to reduce the peaks and valleys that create Mura and downstream stress.
Question 3: Which Lean principle directly addresses why a pull system is preferred over a push system?
- Standardize work to reduce variation
- Produce only what the customer pulls, eliminating overproduction (Correct answer)
- Map the value stream to identify all waste
- Define value from the customer's perspective
Correct answer: Produce only what the customer pulls, eliminating overproduction
A pull system produces goods in response to actual customer demand, which directly prevents overproduction — the most harmful of the eight wastes.
Question 4: During a kaizen event, a team reduces changeover time from 90 minutes to 12 minutes. Which Lean tool did they most likely use?
- Kanban
- 5S
- SMED (Single-Minute Exchange of Die) (Correct answer)
- Poka-yoke
Correct answer: SMED (Single-Minute Exchange of Die)
SMED is specifically designed to reduce equipment changeover or setup times, enabling smaller batch sizes and greater production flexibility.
Question 5: In value stream mapping, what symbol typically represents a 'push' arrow between processes?
- A straight arrow with a solid head
- A striped or wavy push arrow (Correct answer)
- A lightning bolt indicating electronic signals
- A pull arrow curved upward
Correct answer: A striped or wavy push arrow
In VSM convention, a striped push arrow indicates that material is being pushed forward by the upstream process rather than pulled by downstream need.
Question 6: What does the 'takt time' calculation require as inputs?
- Machine cycle time and number of workers
- Available production time and customer demand quantity (Correct answer)
- Lead time and work-in-process inventory levels
- Defect rate and inspection frequency
Correct answer: Available production time and customer demand quantity
Takt time = Available Production Time ÷ Customer Demand, giving the maximum time allowed per unit to meet customer requirements.
Question 7: A Green Belt notices that workers perform the same task differently each shift, causing variable output quality. Which Lean countermeasure directly addresses this?
- Implementing a kanban system
- Creating and enforcing standardized work instructions (Correct answer)
- Applying the pull principle to downstream processes
- Reducing batch sizes with SMED
Correct answer: Creating and enforcing standardized work instructions
Standardized work documents the best current method so every operator performs tasks consistently, reducing variability caused by individual differences.
Lean Six Sigma Green Belt Certification Core Lean Principles 4
What is Mura in Lean, and how does it differ from Muda?