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CUET-PG Statistical Quality Control & Reliability: practice questions

CUET-PG - Statistics · India · National Testing Agency

Original practice questions written to the published syllabus · not past papers
10worked here, free
63written to this exam in this subject
10syllabus units

What this subject covers

Monitoring and accepting quality: Shewhart charts for variables and attributes, CUSUM and EWMA charts, process capability, acceptance sampling plans with their OC, AOQ and ATI curves, and reliability models, applied to seed testing, food processing and input quality. The Agricultural Engineering track covers control charts briefly; this is the full subject.

In the exams: UPSC ISS Statistics III (heavy, reported); SSC CGL JSO (present); AICE-JRF Dairy Microbiology syllabus names 'statistical quality control' (present); light in AICE-JRF Ag Stat

Where the 63 questions fall

How our questions for CUET-PG spread across the units of Statistical Quality Control & Reliability. Difficulty: 20 easy, 39 medium, 4 hard.

Reliability: hazard rate, series and parallel systems, life testing9
Control charts for variables: X-bar, R and s charts7
Control charts for attributes: p, np, c and u charts7
CUSUM and EWMA charts7
Acceptance sampling by attributes: single, double and sequential plans7
Chance and assignable causes of variation6
OC, AOQ, AOQL, ASN and ATI curves6
Acceptance sampling by variables5
Six Sigma and design for quality (introduction)5
Process capability indices4

10 practice questions, worked

Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.

1 · Control charts for variables: X-bar, R and s charts · easy

For subgroups of 5 with R̄ = 0.40 kg, D₃ = 0 and D₄ = 2.114. What is the R chart upper limit?

  1. 0.846 kg
  2. 1.20 kg
  3. 0.231 kg
  4. 0.400 kg
Answer and working

A. 0.846 kg

UCL = D₄R̄ = 2.114 × 0.40 = 0.846; LCL = 0.

Further reading: Montgomery, Introduction to Statistical Quality Control; Duncan, Quality Control and Industrial Statistics; Schilling and Neubauer, Acceptance Sampling in Quality Control

2 · Control charts for variables: X-bar, R and s charts · easy

With R̄ = 0.40 kg from subgroups of 5 (d₂ = 2.326), what is σ̂?

  1. 0.179 kg
  2. 0.172 kg
  3. 0.400 kg
  4. 0.930 kg
Answer and working

B. 0.172 kg

σ̂ = R̄/d₂ = 0.40/2.326 = 0.172.

Further reading: Montgomery, Introduction to Statistical Quality Control; Duncan, Quality Control and Industrial Statistics; Schilling and Neubauer, Acceptance Sampling in Quality Control

3 · Control charts for variables: X-bar, R and s charts · medium

Only one moisture reading per batch is available. Which chart is used?

  1. Individuals and moving-range charts
  2. s chart
  3. X̄ and R chart with n = 1
  4. p chart
Answer and working

A. Individuals and moving-range charts

With n = 1 no within-subgroup range exists; the moving range of successive values estimates σ (MR̄/1.128).

Further reading: Montgomery, Introduction to Statistical Quality Control; Duncan, Quality Control and Industrial Statistics; Schilling and Neubauer, Acceptance Sampling in Quality Control

4 · Control charts for attributes: p, np, c and u charts · medium

With p̄ = 0.04, how large must n be for the p chart to have a positive lower limit?

  1. More than 100
  2. More than 9
  3. More than 216
  4. More than 25
Answer and working

C. More than 216

LCL > 0 requires p̄ > 3√[p̄(1 − p̄)/n], i.e. n > 9(1 − p̄)/p̄ = 216.

Further reading: Montgomery, Introduction to Statistical Quality Control; Duncan, Quality Control and Industrial Statistics; Schilling and Neubauer, Acceptance Sampling in Quality Control

5 · CUSUM and EWMA charts · medium

An EWMA uses λ = 0.2 and L = 3. What are its steady-state limits?

  1. μ₀ ± 3σ
  2. μ₀ ± 0.2σ
  3. μ₀ ± σ
  4. μ₀ ± 0.6σ
Answer and working

C. μ₀ ± σ

Lσ√[λ/(2 − λ)] = 3σ√(0.2/1.8) = 3σ/3 = σ.

Further reading: Montgomery, Introduction to Statistical Quality Control; Duncan, Quality Control and Industrial Statistics; Schilling and Neubauer, Acceptance Sampling in Quality Control

6 · CUSUM and EWMA charts · medium

A dairy laboratory has one fat reading per batch, slightly skewed, and wants to detect slow drifts. Which chart suits it?

  1. A p chart with n = 1
  2. An R chart
  3. An EWMA chart
  4. A c chart
Answer and working

C. An EWMA chart

EWMA averaging makes it robust to mild non-normality and sensitive to small drifts with individual data.

Further reading: Montgomery, Introduction to Statistical Quality Control; Duncan, Quality Control and Industrial Statistics; Schilling and Neubauer, Acceptance Sampling in Quality Control

7 · Acceptance sampling by variables · medium

Which international standard provides variables plans matched to ISO 2859?

  1. ISO 14001
  2. ISO 3951
  3. ISO 22000
  4. ISO 9001
Answer and working

B. ISO 3951

ISO 3951 covers inspection by variables; ISO 9001 is a management-system standard.

Further reading: Montgomery, Introduction to Statistical Quality Control; Duncan, Quality Control and Industrial Statistics; Schilling and Neubauer, Acceptance Sampling in Quality Control

8 · Reliability: hazard rate, series and parallel systems, life testing · easy

Three components with reliabilities 0.95, 0.98 and 0.99 are in series. What is the system reliability?

  1. 0.922
  2. 0.973
  3. 0.950
  4. 0.999990
Answer and working

A. 0.922

Series: product = 0.922. 0.999999 is the parallel arrangement.

Further reading: Montgomery, Introduction to Statistical Quality Control; Duncan, Quality Control and Industrial Statistics; Schilling and Neubauer, Acceptance Sampling in Quality Control

9 · Reliability: hazard rate, series and parallel systems, life testing · medium

A pump with reliability 0.95 is duplicated in parallel. What is the reliability of the pump stage?

  1. 0.95
  2. 0.9975
  3. 0.9025
  4. 0.975
Answer and working

B. 0.9975

Parallel: 1 − (0.05)² = 0.9975; 0.9025 is the series value.

Further reading: Montgomery, Introduction to Statistical Quality Control; Duncan, Quality Control and Industrial Statistics; Schilling and Neubauer, Acceptance Sampling in Quality Control

10 · Reliability: hazard rate, series and parallel systems, life testing · hard

Three identical sensors (reliability 0.9 each) form a 2-out-of-3 system. What is its reliability?

  1. 0.972
  2. 0.900
  3. 0.729
  4. 0.999
Answer and working

A. 0.972

P(at least 2 work) = 3(0.9)²(0.1) + 0.9³ = 0.243 + 0.729 = 0.972.

Further reading: Montgomery, Introduction to Statistical Quality Control; Duncan, Quality Control and Industrial Statistics; Schilling and Neubauer, Acceptance Sampling in Quality Control

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Read the subject

Statistical Quality Control & ReliabilityThe full study manual, free CUET-PGFormat, sections and how it has changed

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Statistical Quality Control & Reliability for other exams

State statistical services · IndiaIndian Statistical Service Examination · IndiaGATE · IndiaIIT JAM · IndiaASRB Agricultural Research Service · IndiaASRB NET · IndiaIndian Statistical Institute admission tests · IndiaICAR AIEEA-PG · IndiaSSC Combined Graduate Level · India

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