8. The time (in minutes) that it takes a car mechanic to replace a car battery is a random variable X that follows an exponential distribution with mean 15 minutes. a) Find P(14 < X < 22). Round off your answer to two decimal places. x 22 1 P(14 < X <22) = √₂/1² 15 e 15dx = P(x < 22) — P(x < 14) x 15 122 = e 15 22 1 - e 14 or 0.8 = = 22 14 = −e 15 + e15 = 0.16254≈ 0.16 - (1 – b) Find the 80th percentile. Round off to the nearest whole number. 1 X S 15 14 e 15 t e 15 dt X 0.8 = 1 e 15 X e 15 = = 0.2 14 22 = e 15 e 15 = 0.16 x — = ln (0.2). This gives x = 24.14156 15

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Chapter1: Combinatorial Analysis
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8. The time (in minutes) that it takes a car mechanic to replace a car battery is a random
variable X that follows an exponential distribution with mean 15 minutes.
a) Find P(14 < X < 22). Round off your answer to two decimal places.
x
22 1
P(14 < X <22) = √₂/1² 15 e 15dx =
P(x < 22) — P(x < 14)
x
15 122
=
e 15
22
1 - e 14
or
0.8 =
=
22
14
= −e 15 + e15 = 0.16254≈ 0.16
- (1 –
b) Find the 80th percentile. Round off to the nearest whole number.
1
X
S
15
14
e 15
t
e 15 dt
X
0.8 = 1 e 15
X
e 15 = = 0.2
14
22
= e 15 e 15 = 0.16
x
— = ln (0.2). This gives x = 24.14156
15
Transcribed Image Text:8. The time (in minutes) that it takes a car mechanic to replace a car battery is a random variable X that follows an exponential distribution with mean 15 minutes. a) Find P(14 < X < 22). Round off your answer to two decimal places. x 22 1 P(14 < X <22) = √₂/1² 15 e 15dx = P(x < 22) — P(x < 14) x 15 122 = e 15 22 1 - e 14 or 0.8 = = 22 14 = −e 15 + e15 = 0.16254≈ 0.16 - (1 – b) Find the 80th percentile. Round off to the nearest whole number. 1 X S 15 14 e 15 t e 15 dt X 0.8 = 1 e 15 X e 15 = = 0.2 14 22 = e 15 e 15 = 0.16 x — = ln (0.2). This gives x = 24.14156 15
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