Probability and Statistics Civil Engineering (CE) Notes | EduRev

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Civil Engineering (CE) : Probability and Statistics Civil Engineering (CE) Notes | EduRev

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Q. 1 The probability density function of a continuous random variable distributed uniformly between x and y (for y > x) is    [2019 : 2 Marks, Set-II]

(a) y - x
(b) Probability and Statistics Civil Engineering (CE) Notes | EduRev

(c) ) x - y

(d) Probability and Statistics Civil Engineering (CE) Notes | EduRev

Ans:  (b)

Probability density function of uniform distribution is
Probability and Statistics Civil Engineering (CE) Notes | EduRev


Q. 2 Probability (up to one decimal place) of consecutively picking 3 red balls without replacement from a box containing 5 red balls and 1 white ball is _______ .    [2018 : 1 Mark, Set-II]
Ans (0.5)

Probability Probability and Statistics Civil Engineering (CE) Notes | EduRev


Q. 3  The graph of a funotion f{x) is shown in the figure

Probability and Statistics Civil Engineering (CE) Notes | EduRev

For f(x) to be valid probability density function, the value of h is     

 [2018 : 1 Mark, Set-II]
(a) 1/3
(b) 2/3
(c) 
(d) 3

Ans (a)

Probability and Statistics Civil Engineering (CE) Notes | EduRev


Q. 4 A probability distribution with right skew is shown in the figure.

Probability and Statistics Civil Engineering (CE) Notes | EduRev

The correct statement for the probability distribution is 
(a) Mean is equal to mode
(b) Mean is greater than median but less than mode 
(c) Mean is greater than median and mode
(d) Mode is greater than median.          [2018 :1 Mark, Set-II]

Ans (c)

Probability and Statistics Civil Engineering (CE) Notes | EduRev

tL < fmea = Curve is skew to right,
mode < mean  
i.e., mean > median and mode
Mean is greater than the mode and the median. This is common for a distribution that is skewed, to the right [i.e., bunched up toward the left and a ‘tail’ stretching toward the right].


Q. 5 For the function f(x) = a + bx, 0 ≤ x ≤ 1, to be a valid probability density function, which one of the following statements is correct?
(a) a = 1, b = 4
(b) a = 0.5, b = 1
(c) a = 0, b = 1
(d)a  = 1, b = 1               [2017 : 2 Marks, Set-I]

Ans: (b)

Probability and Statistics Civil Engineering (CE) Notes | EduRev


Q. 6 The number of parameters in the univariate exponential and Gaussian distributions, respectively, are 

(a) 2 and 2
(b) 1 and 2
(c) 2 and 1
(d) 1 and 1         [2017 : 1 Mark, Set-I]
Ans (b)

In exponential,

Probability and Statistics Civil Engineering (CE) Notes | EduRev   x = 0

The parameter is λ.

In Gaussin
Probability and Statistics Civil Engineering (CE) Notes | EduRev
The parameters are µ and α.
Therefore, answer is (b).


Q. 7 If f(x) arid y(x) are two probability density functions,

Probability and Statistics Civil Engineering (CE) Notes | EduRev

Probability and Statistics Civil Engineering (CE) Notes | EduRev

Which one of the following statements is true?
(a) Mean of f(x) and g(x) are same; Variance of f{x) and g(x) are same

(b) Mean of f(x) and g(x) are same; Variance of f(x) and g(x) are different

(c) Mean of f(x) and g(x) are different; Variance of f(x) and g(x) are same

(d) Mean of f(x) and g(x) are different; Variance of f(x) and g(x) are different

Ans (b)

Mean of f(x) is t(x)
Probability and Statistics Civil Engineering (CE) Notes | EduRev

Variance of f(x) is E(x)2 - {E(x)2} where

Probability and Statistics Civil Engineering (CE) Notes | EduRev

⇒ Variance is a3/6

Next, mean of g(x) is E(x)

Probability and Statistics Civil Engineering (CE) Notes | EduRev

Variance of g(x) is E(x2) - {E(x)}2, where,

Probability and Statistics Civil Engineering (CE) Notes | EduRev

⇒ Variance is a3/2

∴ Mean of f(x) and g(x) are same but variance of f(x) and g(x) are different


Q. 8 X and T are two random independent events. It is known that P (X ) = 0.40 and P { X ∪ Yc ) = 0.7. Which one of the following is the value of P (X ∪ Y)?    [2016 : 1 Mark, Set-II]
(a) 0.7
(b) 0.5
(c) 0.4
(d) 0.3

Ans (a)

Probability and Statistics Civil Engineering (CE) Notes | EduRev

(Since X, Y are independent events)
Probability and Statistics Civil Engineering (CE) Notes | EduRev


Q. 9 Probability density function of a random variable X is given below

Probability and Statistics Civil Engineering (CE) Notes | EduRev       [2016 : 2 Marks, Set-I]

(a) 3/4

(b) 1/4

(c) 1/4

(d) 1/8
Ans   (a)

Probability and Statistics Civil Engineering (CE) Notes | EduRev


Q. 10  The probability density function of a random variable, x is

Ans:Probability and Statistics Civil Engineering (CE) Notes | EduRev


The mean, μx of the random variable is________   [2015 : 2 Marks, Set-11]

Ans: 1.066

Probability and Statistics Civil Engineering (CE) Notes | EduRev

Probability and Statistics Civil Engineering (CE) Notes | EduRev


Q. 11  Consider the following probability mass function (p.m.f.) of a random variable X.
Probability and Statistics Civil Engineering (CE) Notes | EduRev

if  q = 0.4, the variance of X is __________

Ans:  0.24

Given

Probability and Statistics Civil Engineering (CE) Notes | EduRev

Required value = V(X) = E{X2) - [E{X)]2

Probability and Statistics Civil Engineering (CE) Notes | EduRev


Q. 12 A traffic office im poses on an average 5 number of penalties daily on traffic violators. Assume that the number of penalties on different days is independent and follows a Poisson distribution. The probability that there will be less than 4 penalties in a day is __________ .         [2014 : 2 Marks, Set-I

Ans: 0.265

Mean λ, = 5

P(x < 4) = { p(x = 0) + p(x = 1) + p(x = 2) + p(x = 3)}

Probability and Statistics Civil Engineering (CE) Notes | EduRev


Q. 13 A fair (unbiased) coin was tossed four times in succession and resulted in the following outcomes: (i) Head, (ii) Head, (iii) Head, (iv) Head. The probability of obtaining a 'Tail' when the coin is tossed again is

(a) 0
(b) 1/2
(c) 4/5
(d) 1/5
Ans: b

Probability and Statistics Civil Engineering (CE) Notes | EduRev


Q. 14  The probability density function of evaporation E on any day during a year in a watershed is given by 

Probability and Statistics Civil Engineering (CE) Notes | EduRev

The probability that Elies in between 2 and 4 mm/day in a day in the watershed is (in decimal)_____ .         [2014 : 1 Mark, Set-I]

Ans: 0.4

Probability and Statistics Civil Engineering (CE) Notes | EduRev


Q. 15 Find the value of λ such that function f(x) is valid probability density function f(x) = λ(x - 1) ( 2 - x) for 1 ≤ x ≤ 2 = 0 otherwise    [2013 : 2 Marks]

Ans: 6

Probability and Statistics Civil Engineering (CE) Notes | EduRev

Probability and Statistics Civil Engineering (CE) Notes | EduRev


Q. 17 In an experiment, positive and negative values are equally likely to occur. The probability of obtaining at most one negative value in five trials is (a) 1/32 

(b) 2/32 

(c) 3/32 

(d) 6/32        [2011 : 2 Marks

Ans: d

Since negative and positive are equally likely, the distribution of number of negative values is binomial with n = 5 and p = 1/2
Let X represent number of negative values in 5 trials.
p(at most 1 negative value

Probability and Statistics Civil Engineering (CE) Notes | EduRev


Q. 18  The annual precipitation data of a city is normally distributed with mean and standard deviation as 1000 mm and 200 mm, respectively. The probability that the annual precipitation will be more than 1200 mm is
(a) <50%
(b) 50%
(c) 75%
(d) 100%   [2011 : 2 Marks]

Ans: a

The annual precipitation is normally distributed with μ = 1 000 mm and σ = 200 mm

Probability and Statistics Civil Engineering (CE) Notes | EduRev

Where z is the standard normal variate.

In normal distribution Now, since p(-1 < z < 1) ≈ 0.68

(≈ 68% of data is within one standard deviation of mean)

Probability and Statistics Civil Engineering (CE) Notes | EduRev


Q. 19 There are two containers, with one containing 4 red and 3 green balls and the other containing 3 blue and 4 green balls. One ball is drawn at random from each container. The probability that one of the balls is red and the other is blue will be
(a) 1/7
(b) 9/49
(c) 12/49
(d) 3/7       [2011 : 1 Mark]
Ans: c

p(one ball is Red & another is blue)
= p(first is Red and second is Blue)

Probability and Statistics Civil Engineering (CE) Notes | EduRev


Q. 20 Two coins are simultaneously tossed. The probability of two heads sim ultaneously appearing is       [2010 : 1 Mark]
(a) 1/8
(b) 1/6
(c) 1/4
(d) 1/2
Ans:  c

Probability and Statistics Civil Engineering (CE) Notes | EduRev

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