please help me answer (c) and (d)

A First Course in Probability (10th Edition)
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Chapter1: Combinatorial Analysis
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please help me answer (c) and (d)

The two-parameter gamma distribution can be generalized by introducing a third parameter y, called a threshold or location parameter: replace x in (4.8),
f(x; a) =
mean
xa-¹e-x
Γ(α)
0
f(x; a, B) 4
1.0-
0.5-
by x - y and x > 0 by x 2 y. This amounts to shifting the density curves in the figure below so that they begin their ascent or descent at y rather than 0.
f(x; α,) t
1.0-
·α = 1
K
₁α = .6
0.5-
α = 2
0
4 5
(b) standard gamma density curves
0
x ≥ 0
otherwise
-α = 2, B = ₁
1
2
(a) gamma density curves
a = 1, B = 1
T
3
(4.7)
a = 2, ß = 2
4
T
5
a=2, B = 1
6
7
X
A study employs this distribution to model X = 3-day flood volume (108 m³). Suppose that values of the parameters are a = 12, ß = 6, y = 42 (very close to estimates in the cited article based on past data).
(a) What are the mean value and standard deviation of X? (Round your answers to four decimal places.)
114
✓ 108m³
10 m³
standard deviation 20.7846
(b) What is the probability that flood volume is between 100 and 155? (Round your answer to three decimal places.)
.696✔
α = 5
(c) What is the probability that flood volume exceeds its mean value by more than one standard deviation? (Round your answer to three decimal places.)
(d) What is the 95th percentile of the flood volume distribution? (Round your answer to two decimal places.)
108 m³
Transcribed Image Text:The two-parameter gamma distribution can be generalized by introducing a third parameter y, called a threshold or location parameter: replace x in (4.8), f(x; a) = mean xa-¹e-x Γ(α) 0 f(x; a, B) 4 1.0- 0.5- by x - y and x > 0 by x 2 y. This amounts to shifting the density curves in the figure below so that they begin their ascent or descent at y rather than 0. f(x; α,) t 1.0- ·α = 1 K ₁α = .6 0.5- α = 2 0 4 5 (b) standard gamma density curves 0 x ≥ 0 otherwise -α = 2, B = ₁ 1 2 (a) gamma density curves a = 1, B = 1 T 3 (4.7) a = 2, ß = 2 4 T 5 a=2, B = 1 6 7 X A study employs this distribution to model X = 3-day flood volume (108 m³). Suppose that values of the parameters are a = 12, ß = 6, y = 42 (very close to estimates in the cited article based on past data). (a) What are the mean value and standard deviation of X? (Round your answers to four decimal places.) 114 ✓ 108m³ 10 m³ standard deviation 20.7846 (b) What is the probability that flood volume is between 100 and 155? (Round your answer to three decimal places.) .696✔ α = 5 (c) What is the probability that flood volume exceeds its mean value by more than one standard deviation? (Round your answer to three decimal places.) (d) What is the 95th percentile of the flood volume distribution? (Round your answer to two decimal places.) 108 m³
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