1The expected value of a continuous random variable with probability density function is given by:
A.
B.
C.
D.
Correct Answer:
Explanation:
The expected value (or mean) of a continuous random variable is the integral of weighted by the probability density function over the entire range.
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2If is a random variable and is a constant, what is ?
A.
B.$0$
C.
D.$1$
Correct Answer:
Explanation:
The expected value of a constant is the constant itself, as it does not vary.
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3Given a random variable and constants and , what is ?
A.
B.
C.
D.
Correct Answer:
Explanation:
The expectation operator is linear. Therefore, .
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4If is a function of a continuous random variable , the expected value is calculated as:
A.
B.
C.
D.
Correct Answer:
Explanation:
This is known as the Law of the Unconscious Statistician. We integrate the function weighted by the PDF of the original variable .
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5The -th moment of a random variable about the origin is denoted by and is defined as:
A.
B.
C.
D.
Correct Answer:
Explanation:
The moment about the origin is simply the expectation of the random variable raised to the power .
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6The first moment about the origin, , represents the:
A.Variance
B.Mean
C.Kurtosis
D.Skewness
Correct Answer: Mean
Explanation:
The first moment about the origin is , which is the mean or expected value.
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7The -th central moment is defined as:
A.
B.
C.
D.
Correct Answer:
Explanation:
Central moments are moments taken about the mean ( or ). Thus .
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8The second central moment is commonly known as the:
A.Mean
B.Standard Deviation
C.Mean Square Value
D.Variance
Correct Answer: Variance
Explanation:
The second central moment is , which is the definition of Variance.
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9Which of the following relationships relates the variance , the mean square value , and the mean ?
A.
B.
C.
D.
Correct Answer:
Explanation:
Variance is defined as .
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10What is the value of the first central moment, ?
A.
B.
C.$1$
D.$0$
Correct Answer: $0$
Explanation:
.
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11For a random variable and constants , the variance is equal to:
A.
B.
C.
D.
Correct Answer:
Explanation:
Variance is invariant to shifts (adding ) but scales quadratically with the multiplicative constant . Thus, .
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12Skewness is a measure of:
A.The asymmetry of the probability distribution
B.The spread of the distribution
C.The central tendency
D.The peakedness of the distribution
Correct Answer: The asymmetry of the probability distribution
Explanation:
Skewness measures the lack of symmetry. A symmetric distribution has a skewness of 0.
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13The coefficient of skewness is defined using the third central moment and standard deviation as:
A.
B.
C.
D.
Correct Answer:
Explanation:
Skewness is the third standardized moment, calculated as .
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14Kurtosis relates to which central moment?
A.Fourth
B.Second
C.First
D.Third
Correct Answer: Fourth
Explanation:
Kurtosis is a measure of the 'tailedness' or peakedness of the distribution and is based on the fourth central moment .
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15If a PDF is symmetric about its mean, then all odd order central moments are:
A.Positive
B.Infinite
C.One
D.Zero
Correct Answer: Zero
Explanation:
For a symmetric distribution about the mean, the integral on the left cancels the integral on the right for odd powers, resulting in zero.
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16Chebyshev's Inequality provides a bound on probability for:
A.Only Normal distributions
B.Only Exponential distributions
C.Only Discrete distributions
D.Any random variable with finite mean and variance
Correct Answer: Any random variable with finite mean and variance
Explanation:
Chebyshev's Inequality is a distribution-free bound applicable to any RV with a finite mean and variance.
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17According to Chebyshev's Inequality, is less than or equal to:
A.
B.
C.
D.
Correct Answer:
Explanation:
The inequality states that the probability that a value lies at or beyond standard deviations from the mean is at most .
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18Using Chebyshev's inequality, what is the lower bound for the probability that lies within $2$ standard deviations of the mean ()?
A.$0.95$
B.$0.50$
C.$0.25$
D.$0.75$
Correct Answer: $0.75$
Explanation:
The probability is . For , .
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19The Characteristic Function of a random variable is defined as:
A.
B.
C.
D.
Correct Answer:
Explanation:
The characteristic function is the expected value of (Fourier transform of the PDF with a sign reversal in the exponent convention often used in probability).
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20The value of the characteristic function at the origin, , is always:
A.
B.Undefined
C.$0$
D.$1$
Correct Answer: $1$
Explanation:
.
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21The maximum absolute value of the characteristic function is:
A.Equal to variance
B.
C.
D.Infinite
Correct Answer:
Explanation:
.
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22If is the characteristic function of , the -th moment of can be found by:
A.
B.
C.
D.
Correct Answer:
Explanation:
Since , differentiating times brings down . Setting and dividing by gives .
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23The Moment Generating Function (MGF) is defined as:
A.
B.
C.
D.
Correct Answer:
Explanation:
The MGF is the expected value of the exponential of the random variable variable multiplied by a real parameter .
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24Using the MGF , the -th moment is calculated as:
A.
B.
C.
D.
Correct Answer:
Explanation:
The -th moment is the -th derivative of the MGF with respect to , evaluated at .
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25Unlike the characteristic function, the moment generating function:
A.Is always complex-valued
B.Has a maximum value of 0
C.Always exists for all distributions
D.May not exist if the integral diverges
Correct Answer: May not exist if the integral diverges
Explanation:
The CF always exists because the integral of a bounded oscillatory function converges. The MGF involves a real exponential which can grow indefinitely, so the integral may not converge for some distributions (e.g., Cauchy).
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26If , and is the MGF of , then is:
A.
B.
C.
D.
Correct Answer:
Explanation:
.
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27The characteristic function of the sum of two independent random variables is:
A.The product of their characteristic functions
B.The difference of their characteristic functions
C.The convolution of their characteristic functions
D.The sum of their characteristic functions
Correct Answer: The product of their characteristic functions
Explanation:
For independent and , . Thus, the CFs are multiplied.
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28Given a transformation , if is a monotonic differentiable function, the PDF of , , is given by:
A.
B.
C.
D.
Correct Answer:
Explanation:
This is the fundamental transformation formula for PDFs involving the Jacobian of the inverse transformation.
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29If and is a continuous random variable, then is:
A.
B.
C.
D.
Correct Answer:
Explanation:
Here , so . The derivative . Thus .
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30Consider the transformation . If the PDF of is , what is for ?
A.
B.
C.
D.
Correct Answer:
Explanation:
Since is not monotonic (two values map to one ), we sum the contributions from and . The derivative adjustment is .
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31For a linear transformation , the mean is:
A.
B.
C.
D.
Correct Answer:
Explanation:
This follows from the linearity of expectation: .
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32For a linear transformation , the standard deviation is:
A.
B.
C.
D.
Correct Answer:
Explanation:
Variance scales by , so standard deviation (square root of variance) scales by . The shift does not affect spread.
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33If the characteristic function of is , then has which distribution?
A.Exponential
B.Poisson
C.Gaussian (Normal) with mean 0
D.Uniform
Correct Answer: Gaussian (Normal) with mean 0
Explanation:
The function is the standard form of the CF for a Zero-mean Gaussian random variable.
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34The second derivative of the Moment Generating Function at yields:
A.Mean Square Value ()
B.Mean
C.Skewness
D.Variance
Correct Answer: Mean Square Value ()
Explanation:
.
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35Which inequality states that for a non-negative random variable , ?
A.Markov's Inequality
B.Chebyshev's Inequality
C.Jensen's Inequality
D.Cauchy-Schwarz Inequality
Correct Answer: Markov's Inequality
Explanation:
Markov's inequality provides an upper bound for the tail probability of a non-negative random variable based on its mean.
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36If is a discrete random variable with PMF , the expected value is:
A.
B.
C.
D.
Correct Answer:
Explanation:
For discrete variables, expectation is the sum of products of outcomes and their probabilities.
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37If the variance of is zero, then:
A. is uniformly distributed
B.
C. is a constant with probability 1
D. does not exist
Correct Answer: is a constant with probability 1
Explanation:
Zero variance means there is no spread; the variable takes a single value (its mean) with certainty.
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38If , how are the characteristic functions related?
A.
B.
C.
D.
Correct Answer:
Explanation:
.
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39The Maclaurin series expansion of the Characteristic Function generates coefficients related to:
A.Probabilities
B.Central moments
C.Standard deviation
D.Moments about the origin multiplied by
Correct Answer: Moments about the origin multiplied by
Explanation:
. The coefficients involve the moments .
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40Let be a random variable with mean and variance . Using Chebyshev's inequality, is at most:
A.
B.
C.
D.
Correct Answer:
Explanation:
Here . Since , . The bound is .
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41The characteristic function of a standard normal random variable is:
A.
B.
C.
D.
Correct Answer:
Explanation:
For , . The CF is .
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42Which property allows us to recover the PDF from the Characteristic Function?
A.Differentiation
B.Inverse Fourier Transform
C.Convolution
D.Integration
Correct Answer: Inverse Fourier Transform
Explanation:
Since the CF is the Fourier Transform of the PDF (with sign convention adjustment), the PDF is retrieved via the Inverse Fourier Transform.
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43For a random variable , the quantity is called:
A.Mean
B.Root Mean Square (RMS)
C.Variance
D.Standard Deviation
Correct Answer: Root Mean Square (RMS)
Explanation:
The square root of the second moment about the origin is the RMS value.
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44If for , what is ?
A.$0$
B.$1$
C.$2$
D.$0.5$
Correct Answer: $1$
Explanation:
. .
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45The skewness of the normal distribution is:
A.
B.$1$
C.$0$
D.$3$
Correct Answer: $0$
Explanation:
The normal distribution is perfectly symmetric about the mean, so its skewness is 0.
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46If is Uniformly distributed in , then follows which distribution?
A.Exponential
B.Normal
C.Rayleigh
D.Uniform
Correct Answer: Exponential
Explanation:
This is a classic transformation. , which is the CDF of an Exponential distribution.
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47The cumulant generating function is defined as:
A.
B.
C.
D.
Correct Answer:
Explanation:
The cumulant generating function is the natural logarithm of the moment generating function.
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48What is the relation between the second cumulant and the variance?
A.
B.
C.
D.
Correct Answer:
Explanation:
The first cumulant is the mean, and the second cumulant is the variance.
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49If exists, then:
A.Variance is zero
B. and must also exist
C. must also exist
D.The distribution is symmetric
Correct Answer: and must also exist
Explanation:
If a higher order moment exists (is finite), all lower order moments must also exist.
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50For the transformation , where is constant, the PDF is:
A.
B.
C.
D.
Correct Answer:
Explanation:
The graph of the PDF is simply shifted by . If , then . Since , .