Once an individual has been infected with a certain disease, let X represent the time (days) that elapses before the individual becomes infectious. An article proposes a Weibull distribution with
= 2.6,

= 1.5,
and
= 0.5.
[Hint: The two-parameter Weibull distribution can be generalized by introducing a third parameter , called a threshold or location parameter: replace x in the equation below,
f(x; , ) =



x − 1e−(x/) x ≥ 0
0 x < 0
by
x −
and
x ≥ 0
by
x ≥ .]
(a)
Calculate
P(1 < X < 2).
(Round your answer to four decimal places.)
.5763

Correct: Your answer is correct.
(b)
Calculate
P(X > 1.5).
(Round your answer to four decimal places.)
.7058

Correct: Your answer is correct.
(c)
What is the 90th percentile of the distribution? (Round your answer to three decimal places.)
2.567

Correct: Your answer is correct.
days
(d)
What are the mean and standard deviation of X? (Round your answers to three decimal places.)
mean
1.332

Incorrect: Your answer is incorrect.
days
standard deviation
days