An Introduction to Mathematical Statistics and Its Applications (6th Edition)

Published by Pearson
ISBN 10: 0-13411-421-3
ISBN 13: 978-0-13411-421-7

Chapter 4 Special Distributions - 4.3 The Normal Distribution - Questions - Page 243: 5

Answer

(a) $\color{blue}{-0.44} $ (b) $\color{blue}{0.76}$ (c) $\color{blue}{0.41}$ (d) $\color{blue}{1.282\ \text{(interpolated)} \;\approx\; 1.28}$ (e) $\color{blue}{0.949\ \text{(interpolated)} \;\approx\; 0.95}$

Work Step by Step

(a) $\begin{align*} P(Z \le z) &= 0.33 \\ F_Z(z) &= 0.33 \\ F_Z(z) &= F_Z(-0.44) \qquad \text{[ see Appendix Table A.1, pp. 675-6 ]} \\ z &\color{blue}{= -0.44} \qquad \text{[ since}\ F_Z(z)\ \text{is one-to-one for}\ 0 < F_Z(z) < 1\ ] \end{align*}$ (b) $\begin{align*} P(Z \ge z) &= 0.2236 \\ P(Z \gt z) &= 0.2236 \\ P(Z\le z) &= 1-0.2236 \\ F_Z(z) &= 0.7764 \\ F_Z(z) &= F_Z(0.76) \qquad \text{[ see Appendix Table A.1, pp. 675-6 ]} \\ z &\color{blue}{= 0.76} \qquad \text{[ since}\ F_Z(z)\ \text{is one-to-one for}\ 0 < F_Z(z) < 1\ ] \end{align*}$ (c) $\begin{align*} P(-1.00 \le Z \le z) &= 0.5004 \\ P(-1.00 \lt Z \le z) &= 0.5004 \\ P(Z \le z) - P(Z\le -1.00) &= 0.5004 \\ F_Z(z) - F_Z(-1.00) &= 0.5004 \\ F_Z(z) - 0.1587 &= 0.5004 \\ F_Z(z) &= 0.6591 \\ F_Z(z) &= F_Z(0.41) \qquad \text{[ see Appendix Table A.1, pp. 675-6 ]} \\ z &\color{blue}{= 0.41} \qquad \text{[ since}\ F_Z(z)\ \text{is one-to-one for}\ 0 < F_Z(z) < 1\ ] \end{align*}$ (d) $\begin{align*} P(-z \le Z \le z) &= 0.80 \\ 2P(0 \lt Z \le z) &=0.80 \qquad \text{[ since }\ f_z(z)\ \text{is symmetric about}\ x=0\ ] \\ P(0 \lt Z \le z) &= 0.40 \\ P(Z\le 0) + P(0\lt Z\le z) &= 0.50 + 0.40 \qquad \text{[ since }\ P(Z\le 0) = 0.50, Z\sim N(0,1)\ ] \\ P(Z\le z) &= 0.9000 \\ F_Z(z) &= 0.9000 \\ F_Z(z) &= F_Z(1.282) \qquad \text{[ see Appendix Table A.1, pp. 675-6; interpolate ]} \\ z &\color{blue}{= 1.282 \;\approx\; 1.28} \qquad \text{[ since}\ F_Z(z)\ \text{is one-to-one for}\ 0 < F_Z(z) < 1\ ] \end{align*}$ (e) $\begin{align*} P(z \le Z \le 2.03) &= 0.15 \\ P(z\lt Z \le 2.03) &= 0.15 \\ P(Z \le 2.03) - P(Z\le z) &= 0.15 \\ F_Z(2.03) - F_Z(z) &= 0.15 \\ 0.9788 - F_Z(z) &= 0.15 \\ 0.9788 - 0.15 &= F_Z(z) \\ 0.8288 &= F_Z(z) \\ F_Z(0.949) &= F_Z(z) \qquad \text{[ see Appendix Table A.1, pp. 675-6; interpolate ]} \\ z &\color{blue}{= 0.949 \;\approx\; 0.95} \qquad \text{[ since}\ F_Z(z)\ \text{is one-to-one for}\ 0 < F_Z(z) < 1\ ] \end{align*}$
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