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Which of the following distributions is not symmetrical?


A) Exponential
B) Uniform.
C) Normal.
D) None of these choices are correct.

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Given that z is a standard normal random variable, a negative value of z indicates that the standard deviation of z is negative.

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If the random variable X is normally distributed with a mean of 75 and a standard deviation of 8, then P(X ≤ 75) is:


A) 0.125.
B) 0.975.
C) 0.625.
D) 0.500.

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Which of the following is not true for a random variable X that is uniformly distributed over the interval axba \leq x \leq b ?


A) E(X) = (a + b) /2.
B) V(X) = (ba) 2( b - a ) ^ { 2 } /12.
C) σ\sigma = (b - a) /6.
D) f(x) =1/(ba) f ( x ) = 1 / ( b - a ) if a ? x ? b.

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The probability density function f(x) for a uniform random variable X defined over the interval [1, 11] is:


A) any value between 1 and 11.
B) 0.100.
C) 0.091.
D) above 11.

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Given that Z is a standard normal random variable, the mean of Z is:


A) smaller than the median.
B) larger than the mode.
C) always equal to zero.
D) always smaller than zero.

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In the normal distribution, the total area under the curve is equal to one.

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The mean and standard deviation of a normally distributed random variable that has been standardised are one and zero, respectively.

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If the random variable X is exponentially distributed, then which of the following statements best describes the mean of X?


A) The mean of X will be greater than the standard deviation of X.
B) The mean of X will be smaller than the standard deviation of X.
C) The mean of X will equal the standard deviation of X.
D) None of these choices are correct.

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Given that X is a normal variable, which of the following statements is (are) true?


A) The variable X + 5 is also normally distributed.
B) The variable X - 5 is also normally distributed.
C) The variable 5X is also normally distributed.
D) All of these choices are correct.

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Find the following probabilities: a. P(X1)P ( X \leq 1 ) b. P(X2)P ( X \geq 2 ) c. P(1X2)P ( 1 \leq X \leq 2 ) d. P(X=3)P ( X = 3 )

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a. 0.4375....

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In a shopping centre, the waiting time for an elevator is found to be uniformly distributed between 1 and 5 minutes. a. What is the probability density function for this uniform distribution? b. What is the probability of waiting no more than 3 minutes? c. What is the probability that the elevator arrives in the first 30 seconds? d. What is the probability of a waiting time between 2 and 3 minutes? e. What is the expected waiting time?

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a. f(x) = 1/4, 1 F1F...

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If the random variable X is uniformly distributed over the interval 10 \leq x \leq 50, find the following probabilities. a. P(X30)P ( X \geq 30 ) b. P(X25)P ( X \leq 25 ) c. P(18X35)P ( 18 \leq X \leq 35 ) d. P(X=40)P ( X = 40 )

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a. 0.50.
b...

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Consider a binomial random variable X with n = 300 and p = 0.02. Approximate the values of the following probabilities. a. P(X = 4). b. P(X 5). c. P(X 8).

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a. 0.1161....

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The probability density function, f(x) , for any continuous random variable X, represents:


A) all possible values that X will assume within some interval a x b.
B) the probability that X takes on a specific value x.
C) the area under the curve at x.
D) the height of the function at x.

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Using the standard normal curve, the probability or area between z = -1.28 and z = 1.28 is 0.1003

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Given that Z is a standard normal random variable, the area to the left of a value z is expressed as:


A) P(Z \geq z) .
B) P(Z \leq z) .
C) P(0 \leq Z \leq z) .
D) P(Z \geq -z) .

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For a normal curve, if the mean is 20 minutes and the standard deviation is 5 minutes, the area to the right of 13 minutes is 0.9192.

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The expected value, E(X) , of a uniform random variable X defined over the interval axba \leq x \leq b , is:


A) a + b.
B) a - b.
C) (a + b) /2.
D) (a - b) /2.

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Which of the following is always true for all probability density functions of continuous random variables?


A) They are symmetrical.
B) They are bell-shaped.
C) The area under the curve is 1.0.
D) They have the same height.

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