5-3 TWO CONTINUOUS RANDOM VARIABLES 161
The first integral is
The second integral is
Therefore,
Alternatively, the probability can be calculated from the marginal probability distribution of Y
as follows. For
6 10 ^3 e0.002y^11 e0.001y 2 for y
0
610 ^6 e0.002y a
e0.001x
0.001
`
y
0
b 610 ^6 e0.002y a
1 e0.001y
0.001
b
fY 1 y 2
y
0
6 10 ^6 e0.001x0.002y dx 6 10 ^6 e0.002y (^)
y
0
e0.001x^ dx
y
0
P 1 Y
20002 0.04750.00250.05.
6 10 ^6
0.002
a
e^6
0.003
b0.0025
6 10 ^6
2000
°
e0.002y
0.002
`
x
¢ e0.001x dx
610 ^6
0.002
(^)
2000
e0.003x dx
6 10 ^6
0.002
e^4 a
1 e^2
0.001
b0.0475
6 10 ^6
2000
0
°
e0.002y
0.002
`
2000
¢ e0.001x dx
610 ^6
0.002
e^4
2000
0
e0.001x dx
Figure 5-10 Region of integration
for the probability that is
darkly shaded and it is partitioned
into two regions withx 2000 and
x 2000.
Y 2000
y
0 x
0
2000
2000
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