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# Probability calculation using the Z score

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Fill in the P(X = x) values in the table below to give a legitimate probability distribution for the discrete random variable X, whose possible values are -2, -1, 4, 5, and 6.

Value x of X P(X = x)
-2 0.24
-1 0.19
4 0.12
5
6

Let X be a random variable with the following probability distribution
Value x of X P(X = x)
-2 0.10
-1 0.35
0 0.40
1 0.05
2 0.10

Find the expectation E (X) and variance Var (X) of X.
E (x) =
Var (X) =

P (Z > -2.15) =
P (Z < 0.98) =
P ( - 0.78 < Z < 2.20) =

Let Z be a standard normal random variable, Use the calculator provided to determine the value of c such that P ( -c < Z < c)= 0.9512
Carry your intermediate computations to at least four decimal places

Let Z be a standard normal random variable, Use the calculator provided to determine the value of c such that P ( -c < Z < c)= 0.9512
Let Z be a standard normal random variable, Use the calculator provided to determine the value of c such that P ( c < Z < c-1.17)= 0.0954
The scores on a particular test are normally distributed with a mean of 130 and a standard deviation of 15 what is the minimum score needed to be in the top 20% of the scores on the test. Carry your intermediate computations to a least four decimal places , and round your answer to a least one decimal place.

Normal distribution: Word problems
Suppose that the time required to complete a 1040R tax form is normally distributed with a mean of minutes and a standard deviation of minutes. What proportion of 1040R tax forms will be completed in at most minutes? Round your answer to at least four decimal places.

t distribution
Use the calculator provided to solve the following problems.
? Consider a t distribution with degrees of freedom. Compute . Round your answer to at least three decimal places.
? Consider a t distribution with degrees of freedom. Find the value of such that . Round your answer to at least three decimal places.

P (-1.18 < t < 1.18) =
C =

Chi-square distribution
.
? Suppose that follows a chi-square distribution with degrees of freedom. Compute . Round your answer to at least three decimal places.
? Suppose again that follows a chi-square distribution with degrees of freedom. Find such that . Round your answer to at least two decimal places.
? Find the median of the chi-square distribution with degrees of freedom. Round your answer to at least two decimal places.

P (x2 < 16) =
K=
Median =

F distribution
? Consider an F distribution with numerator degrees of freedom and denominator degrees of freedom. Compute . Round your answer to at least three decimal places.
? Consider an F distribution with numerator degrees of freedom and denominator degrees of freedom. Find such that . Round your answer to at least two decimal places.

P ( F < 1.44) =
C =

Central limit theorem: Sample mean
The mean salary offered to students who are graduating from Coastal State University this year is , with a standard deviation of . A random sample of Coastal State students graduating this year has been selected. What is the probability that the mean salary offer for these students is or less?
Carry your intermediate computations to at least four decimal places. Round your answer to at least three decimal places.