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SOLUTIONS MANUAL for Stochastic Modeling: Analysis and ...

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32 CHAPTER 5. ARRIVAL-COUNTING PROCESSES<br />

(b) The expected time between arrivals is<br />

1/λ =1/2 hour<br />

Let G be the gap between two successive arrivals. Then G is exponentially distributed<br />

with λ =2.<br />

Pr{G >1} = 1− Pr{G ≤ 1}<br />

= 1− (1 − e −2(1) )<br />

= e −2<br />

≈ 0.135<br />

(c) Because of the memoryless property<br />

E[R 0 ]=E[G] =1/2 hour<br />

Pr{R 0 ≤ 1/4} =Pr{G ≤ 1/4} =1− e −2(1/4)<br />

≈ 0.393<br />

(d)<br />

Pr{T 13 ≤ 7} =1−<br />

12 ∑<br />

j=0<br />

e −2(7) (2(7)) j<br />

j!<br />

≈ 0.641<br />

(e) Let λ 0 be the arrival rate <strong>for</strong> urgent patients.<br />

λ 0 =0.14λ = 0.28 patients/hour<br />

Pr{Y 0,12 > 6} = 1− Pr{Y 0,12 ≤ 6}<br />

6∑ e −0.28(12) (0.28(12)) j<br />

= 1−<br />

j!<br />

j=0<br />

≈ 0.055<br />

(f) Let λ 2 be the overall arrival rate.<br />

λ 2 = λ +4=6/hour

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