# ISS (Statistical Services) Statistics Paper IV: Questions 28 - 30 of 92

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## Question number: 28

» Statistical Quality Control » Control Charts » Attributes

### Describe in Detail

The following are the figures of defectives in 22 lots each containing 2,000 bulbs. Ind control limit for p-Chart.

425 | 430 | 216 | 341 | 225 | 322 | 280 | 306 | 337 | 305 | 356 |

402 | 216 | 264 | 126 | 409 | 193 | 326 | 280 | 389 | 451 | 420 |

### Explanation

**We have n = 2000**

S. No. | d | |

1 | 425 | 0.2125 |

2 | 430 | 0.215 |

3 | 216 | 0.108 |

4 | 341 | 0.1705 |

… (79 more words) …

## Question number: 29

» Statistical Quality Control » Control Charts » Attributes

### Describe in Detail

Each day a sample of 1500 items from a production process was examined. The number of defectives found in each sample was as follows. With a suitable control chart, check out for control 4,6, 6,2, 15,4, 4

### Explanation

We have n = 30

S. No. | d | |

1 | 4 | 0.00267 |

2 | 6 | 0.00400 |

3 | 6 | 0.00400 |

4 | 2 | 0.00133 |

… (73 more words) …

## Question number: 30

» Statistical Quality Control » Control Charts » Variable

### Describe in Detail

a) The number of customer complaints are recorded at a television manufacturing company. Complaints have been recorded over the past 20 weeks. Construct 3-σ control limits for the *c*-chart.

Week | No. of complaints | Week | No. of complaints |

1 | 0 | 11 | 4 |

2 | 3 | 12 | 3 |

3 | 4 | 13 | 1 |

4 | 1 | 14 | 1 |

5 | 0 | 15 | 1 |

6 | 0 | 16 | 0 |

7 | 3 | 17 | 2 |

8 | 1 | 18 | 1 |

9 | 1 | 19 | 2 |

10 | 0 | 20 | 2 |

b) A machine is manufacturing mica discs. samples of size 5 are drawn every hour and their thickness in units are recorded as follows. From this data construct 3-σ control limits for **chart. **

Sample No. | Observstions | ||||

1 | 8 | 9 | 15 | 4 | 11 |

2 | 7 | 10 | 7 | 6 | 8 |

3 | 11 | 12 | 10 | 9 | 10 |

4 | 12 | 8 | 6 | 9 | 12 |

5 | 11 | 10 | 6 | 14 | 11 |

6 | 7 | 7 | 10 | 4 | 11 |

7 | 10 | 7 | 4 | 10 | 10 |

8 | 8 | 11 | 11 | 7 | 7 |

9 | 8 | 11 | 8 | 14 | 12 |

10 | 12 | 9 | 12 | 17 | 11 |

11 | 7 | 7 | 9 | 17 | 13 |

12 | 9 | 9 | 4 | 4 | 11 |

13 | 10 | 12 | 12 | 12 | 12 |

14 | 8 | 11 | 9 | 6 | 8 |

15 | 10 | 13 | 9 | 4 | 9 |

16 | 9 | 11 | 8 | 5 | 11 |

### Explanation

a) Average number of defects per sample is

=1.5+ =1.5 + 3 (1.22) =5.174

=

… (145 more words) …