7.S.8. Arandomsample of size n = 19 is drnwn from a normal distribution for which a2 = 12.0. In what range are we likely to find the sample variance, *s**2**?** *Answer the question by finding two numbers *a *and *b *such that

*P(a **s *s2 *b) *= 0.95

7.5.9. One of the occupational hazards of being an airplane pilot is I.he hearing loss that results from being exposed to high noise levels. To document the magnitude of the problem, a team of researchers measured the cockpit noise levels in 18 commercial aircraft. The results (in decibels) are as follows (94).

Plane 1 | Noise Level 74 | Plane 10 | Noise Level 72 |

2 | 77 | 11 | 90 |

3 | 80 | 12 | 87 |

4 | 82 | 13 | 73 |

| 82 | 14 | 83 |

6 |
| 15 | 86 |

7 | 80 | 16 | 83 |

8 | 75 | 17 | 83 |

| 75 | 18 | 80 |

(Iii) Assume that coc.kpit noise levels are normally distributed. Use Theorem 7.5.1 to construct a 95% confidence interval for the standard deviation of noise levels ftom plane to plane.

(b) Use these same data lo construct two *one-sided *95% confidence intervals for *a.*

* *

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