GATE Exam 2021 Stastics (ST) Question Paper With Answer Key

GATE-2021

ST: Statistics

GA-General Aptitude

Q.1 – Q.5 Multiple Choice Question (MCQ), carry ONE mark each (for each wrong answer: – 1/3).

1. The current population of a city is 11,02,500. If it has been increasing at the rate of 5% per annum, what was its population 2 years ago?

(A)  9,92,500

(B)  9,95,006

(C)  10,00,000

(D)  12,51,506

Answer: (C)

2. p and q are positive integers and 

(A)  3

(B)  7

(C)  9

(D)  11

Answer: (B)

3. 

The least number of squares that must be added so that the line P-Q becomes the line of symmetry is ________

(A)  4

(B)  3

(C)  6

(D)  7

Answer: (C)

4. Nostalgia is to anticipation as _______ is to ________

Which one of the following options maintains a similar logical relation in the above sentence?

(A)  Present, past

(B)  Future, past

(C)  Past, future

(D)  Future, present

Answer: (C)

5. Consider the following sentences:

(i) I woke up from sleep.

(ii) I woked up from sleep.

(iii) I was woken up from sleep.

(iv) I was wokened up from sleep.

Which of the above sentences are grammatically CORRECT?

(A)  (i) and (ii)

(B)  (i) and (iii)

(C)  (ii) and (iii)

(D)  (i) and (iv)

Answer: (B)

Q.6 – Q. 10 Multiple Choice Question (MCQ), carry TWO marks each (for each wrong answer: – 2/3).

6. Given below are two statements and two conclusions.

Statement 1: All purple are green.

Statement 2: All black are green.

Conclusion I: Some black are purple.

Conclusion II: No black is purple.

Based on the above statements and conclusions, which one of the following options is logically CORRECT?

(A)  Only conclusion I is correct.

(B)  Only conclusion II is correct.

(C)  Either conclusion I or II is correct.

(D)  Both conclusion I and II are correct.

Answer: (C)

7. Computers are ubiquitous. They are used to improve efficiency in almost all fields from agriculture to space exploration. Artificial intelligence (AI) is currently a hot topic. AI enables computers to learn, given enough training data. For humans, sitting in front of a computer for long hours can lead to health issues.

Which of the following can be deduced from the above passage?

(i) Nowadays, computers are present in almost all places.

(ii) Computers cannot be used for solving problems in engineering.

(iii) For humans, there are both positive and negative effects of using computers.

(iv) Artificial intelligence can be done without data.

(A)  (ii) and (iii)

(B)  (ii) and (iv)

(C)  (i), (iii) and (iv)

(D)  (i) and (iii)

Answer: (D)

8. Consider a square sheet of side 1 unit. In the first step, it is cut along the main diagonal to get two triangles. In the next step, one of the cut triangles is revolved about its short edge to form a solid cone. The volume of the resulting cone, in cubic units, is ________

(A)  π/3

(B)  2π/3

(C)  3π/2

(D)  3π

Answer: (A)

9. 

The number of minutes spent by two students, X and Y, exercising every day in a given week are shown in the bar chart above.

The number of days in the given week in which one of the students spent a minimum of 10% more than the other student, on a given day, is

(A)  4

(B)  5

(C)  6

(D)  7

Answer: (C)

10. 

Corners are cut from an equilateral triangle to produce a regular convex hexagon as shown in the figure above.

The ratio of the area of the regular convex hexagon to the area of the original equilateral triangle is

(A)  2 : 3

(B)  3 : 4

(C)  4 : 5

(D)  5 : 6

Answer: (A)

Statistics (ST)

Q.1 – Q.9 Multiple Choice Question (MCQ), carry ONE mark each (for each wrong answer: – 1/3).

1. Let X be a non-constant positive random variable such that E(X) = 9. Then which one of the following statements is true?

Answer: (A)

2. Let {W(t)}t≥0 be a standard Brownian motion. Then the variance of W(1)W(2) equals

(A)  1

(B)  2

(C)  3

(D)  4

Answer: (C)

3. Let X1,X2, … ,Xn be a random sample of size n (≥ 2) from a distributionhaving the probability density function

where θ ∈ (0, ∞). Then the method of moments estimator of θ equals

Answer: (A)

4. Let {x1, x2, … , xn} be a realization of a random sample of size n (≥ 2) from a N(μ,σ2) distribution, where −∞ < μ < ∞ and σ > 0. Which of the following statements is/are true?

P : 95% confidence interval of μ based on {x1, x2, … , xn} is unique when σ is known.

Q : 95% confidence interval of μ based on {x1, x2, … , xn} is NOT unique when σ is unknown.

(A)  P only

(B)  Q only

(C)  Both P and Q

(D)  Neither P nor Q

Answer: (B)

5. Let X1, X2, … , Xn be a random sample of size n (≥ 2) from a N(0, σ2) distribution. For a given σ > 0, let fσ denote the joint probability density function of (X1,X2, … ,Xn) and S = {fσ: σ > 0}. Let  For any positive integer ν and any α ∈ (0, 1), let  denote the (1 − α)-th quantile of the central chi-square distribution with ν degrees of freedom. Consider testing H0: σ = 1 against H1: σ > 1 at level α. Then which one of the following statements is true?

(A)  S has a monotone likelihood ratio in T1 and H0 is rejected if   

(B)  S has a monotone likelihood ratio in T1 and H0 is rejected if   

(C)  S has a monotone likelihood ratio in T2 and H0 is rejected if   

(D)  S has a monotone likelihood ratio in T2 and H0 is rejected if  

Answer: (A)

6. Let X and Y be two random variables such that p11 + p10 + p01 + p00 = 1, where pij = P(X = i, Y = j), i,j = 0, 1. Suppose that a realization of a random sample of size 60 from the joint distribution of (X, Y) gives

n11 = 10, n10 = 20, n01 = 20 and n00 = 10,

where nij denotes the frequency of (i, j) for i, j = 0, 1. If the chi-square test of independence is used to test

H0: pij = pi⋅pj for i, j = 0, 1 against H1: pij ≠ pi⋅pj for at least one pair

where pi = pi0 + pi1 and pj = p0j + p1j, then which one of the following statements is true?

(i,j),

(A)  Under H0, the test statistic follows central chi-square distribution with one degree of freedom and the observed value of the test statistic is 20/3

(B)  Under H0, the test statistic follows central chi-square distribution with three degrees of freedom and the observed value of the test statistic is 20/3

(C)  Under H0, the test statistic follows central chi-square distribution with one degree of freedom and the observed value of the test statistic is 16/3

(D)  Under H0, the test statistic follows central chi-square distribution with three degrees of freedom and the observed value of the test statistic is 16/3

Answer: (A)

7. Let the joint distribution of (X, Y) be bivariate normal with mean vector  and variance-covariance matrix   where −1 < ρ < 1. Let Φρ(0, 0) = P(X ≤ 0, Y ≤ 0). Then the Kendall’s τ coefficient between X and Y equals

(A)  4Φρ(0,0) − 1

(B)  4Φρ(0,0)

(C)  4Φρ(0,0) + 1

(D)  Φρ(0,0)

Answer: (A)

8. Consider the simple linear regression model

Yi = β0 + β1xi + εi, i = 1, 2, … , n (n ≥ 3),

where β0 and β1 are unknown parameters and εi’s are independent and identically distributed random variables with mean zero and finite variance σ2 > 0. Suppose that  are the ordinary least squares estimators of β0 and β1, respectively. Define  and  , where yi 0 is the observed value of Yi, , i = 1, 2, … , n. Then for a real constant c, the variance of  is

Answer: (B)

9. Let X1, X2, X3, Y1, Y2, Y3 and Y4 be independent random vectors such that Xi follows N4(0, Σ1) distribution for i = 1, 2, 3, and Yj follows N4(0, Σ2) distribution for j = 1, 2, 3, 4, where Σ1 and Σ2 are positive definite matrices. Further, let

where X = [X1 X2 X3] is a 4 × 3 matrix, Y = [Y1 Y2 Y3 Y4] is a 4 × 4 matrix and XT and YT denote transposes of X and Y, respectively. If Wm(n, Σ) denotes a Wishart distribution of order m with n degrees of  freedom and variance-covariance matrix Σ and In denotes the n × n identity matrix, then which one of the following statements is true?

(A)  Z follows W4(7,I4) distribution

(B)  Z follows W4(4,I4) distribution

(C)  Z follows W7 (4,I7 ) distribution

(D)  Z follows W7 (7,I7) distribution

Answer: (A)

Q.10 – Q.25 Numerical Answer Type (NAT), carry ONE mark each (no negative marks).

10. 

Answer: (2 to 2)

11. Let 

Then the value of e I1+ π equals __________ (round off to 2 decimal places).

Answer: ()

12. Let  and I3 be the 3 × 3 identity matrix. Then the nullity of 5A(I3 + A  2) equals __________

Answer: (33.50 to 34.50)

13. Let A be the 2 × 2 real matrix having eigenvalues 1 and − 1, with corresponding eigenvectors  respectively. If  then a + b + c + d equals __________ (round off to 2 decimal places).

Answer: (2 to 2)

14. Let A and B be two events such that P(B) = 3/4 and P(A ⋃ BC) = 1/2. If A and B are independent, then P(A) equals __________ (round off to 2 decimal places).

Answer: (1.70 to 1.75)

15. A fair die is rolled twice independently. Let X and Y denote the outcomes of the first and second roll, respectively. Then E(X + Y | (X − Y)2 = 1) equals ________

Answer: (7 to 7)

16. Let X be a random variable having distribution function

where a and c are appropriate constants. Let  n ≥ 1, and  If P(X ≤ 1) = 1/2 and E(X) = 5/3, then P(X ∈ A) equals __________ (round off to 2 decimal places).

Answer: (0.32 to 0.35)

17. If the marginal probability density function of the kth order statistic of a random sample of size 8 from a uniform distribution on [0, 2] is then k equals __________

Answer: (7 to 7)

18. For α > 0, let  be a sequence of independent random variables such that 

Let S = {α > 0 ∶ Xn(a) converges to 0 almost surely as n → ∞}. Then the infimum of S equals __________ (round off to 2 decimal places).

Answer: (0.50 to 0.50)

19. Let {Xn}n≥1 be a sequence of independent and identically distributed random variables each having uniform distribution on [0, 2]. For n ≥ 1, let

Then, as n → ∞, the sequence {Zn}n≥1 converges almost surely to _______ (round off to 2 decimal places).

Answer: (0.27 to 0.35)

20. Let {Xn}n≥0 be a time-homogeneous discrete time Markov chain with state space {0, 1} and transition probability matrix  If P(X0 = 0) = P(X0 = 1) = 0. 5, then  equals ______

Answer: (50 to 50)

21. Let {0, 2} be a realization of a random sample of size 2 from a binomial distribution with parameters 2 and p, where p ∈ (0, 1). To test H0: p = 1/2 against H1: p ≠ 1 the observed value of the likelihood ratio test statistic equals _________ (round off to 2 decimal places).

Answer: (0.98 to 1.00)

22. Let X be a random variable having the probability density function

Then  equals __________ (round off to 2 decimal places).

Answer: (8.60 to 8.75)

23. Let (Y, X1,X2) be a random vector with mean vector and variance-covariance matrix  Then the value of the multiple correlation coefficient between Y and its best linear predictor on X1 and X2 equals _________ (round off to 2 decimal places).

Answer: (0.14 to 0.18)

24. Let  be a random sample from a bivariate normal distribution with unknown mean vector μ and unknown variance-covariance matrix Σ, which is a positive definite matrix. The p-value corresponding to the likelihood ratio  test for testing  based on the realization  of the random sample equals __________ (round off to 2 decimal places).

Answer: (1.00 to 1.00)

25. Let Yi = α + βxi + εi, i = 1, 2, 3, where xi’s are fixed covariates, α and β are unknown parameters and εi’s are independent and identically distributed random variables with mean zero and finite variance. Let  be the ordinary least squares estimators of α and β, respectively. Given the following observations

the value of  equals ________ (round off to 2 decimal places).

Answer: (6.31 to 6.35)

Q.26 – Q.43 Multiple Choice Question (MCQ), carry TWO mark each (for each wrong answer: – 2/3).

26. Let f: ℝ → ℝ be defined by

where ℝ denotes the set of all real numbers, ℤ denotes the set of all integers, ℕ denotes the set of all positive integers and gcd(p, q) denotes the greatest common divisor of p and q. Then which one of the following statements is true?

(A)  f is not continuous at 0

(B)  f is not differentiable at 0

(C)  f is differentiable at 0 and the derivative of f at 0 equals 0

(D)  f is differentiable at 0 and the derivative of f at 0 equals 1

Answer: (C)

27. Let f:[0, ∞) → ℝ be a function, where R denotes the set of all real numbers. Then which one of the following statements is true?

(A)  If f is bounded and continuous, then f is uniformly continuous

(B)  If f is uniformly continuous, then   exists

(C)  If f is uniformly continuous, then the function g(x) = f(x) sin x is also uniformly continuous

(D)  If f is continuous and  is finite, then f is uniformly continuous

Answer: (D)

28. Let f: ℝ → ℝ be a differentiable function such that f(0) = 0 and f′ (x) + 2f(x) > 0 for all x ∈ R, where f′ denotes the derivative of f and R denotes the set of all real numbers. Then which one of the following statements is true?

(A)  f(x) > 0, for all x > 0 and f(x) < 0, for all x < 0

(B)  f(x) < 0, for all x ≠ 0

(C)  f(x) > 0, for all x ≠ 0

(D)  f(x) < 0, for all x > 0 and f(x) > 0, for all x < 0

Answer: (A)

29. Let M be the collection of all 3 × 3 real symmetric positive definite matrices. Consider the set  where 0 denotes the 3 × 3 zero matrix. Then the number of elements in S equals

(A)  0

(B)  1

(C)  8

(D)  ∞

Answer: (B)

30. Let A be a 3 × 3 real matrix such that I3 + A is invertible and let B = (I3 + A)1(I3 – A), where I3 denotes the 3 × 3 identity matrix. Then which one of the following statements is true?

(A)  If B is orthogonal, then A is invertible

(B)  If B is orthogonal, then all the eigenvalues of A are real

(C)  If B is skew-symmetric, then A is orthogonal

(D)  If B is skew-symmetric, then the determinant of A equals −1

Answer: (C)

31. Let X be a random variable having Poisson distribution such thatE(X2) = 110. Then which one of the following statements is NOT true?

(A)  E(Xn) = 10 E[(X + 1)n−1], for all n = 1, 2, 3, …

(B)   

(C)  P(X = k) < P(X = k + 1), for k = 0, 1, … , 8

(D)  P(X = k) > P(X = k + 1), for k = 10, 11, …

Answer: (B)

32. Let X be a random variable having uniform distribution on  Then which one of the following statements is NOT true?

(A)  Y = cot X follows standard Cauchy distribution

(B)  Y = tan X follows standard Cauchy distribution

(C)    has moment generating function  

(D)    follows central chi-square distribution with one degree of freedom

Answer: (D)

33. Let Ω = {1, 2, 3, … } represent the collection of all possible outcomes of a random experiment with probabilities P({n}) = αn for n ∈ Ω. Then which one of the following statements is NOT true?

(A)   

(B)   

(C)  For any positive integer k, there exist k disjoint events A1, A2, … , Ak such that  

(D)  There exists a sequence {Ai}i≥1 of strictly increasing events such that   

Answer: (B)

34. Let (X, Y) have the joint probability density function

Then which one of the following statements is NOT true?

(A)  The probability density function of X + Y is   

(B)  P(X + Y > 4) = 3/4

(C)  E(X + Y) = 4 loge 2

(D)  E(Y | X = 2) = 4

Answer: (C)

35. Let X1, X2 and X3 be three uncorrelated random variables with common variance σ2 < ∞. Let Y1 = 2X1 + X2 + X3, Y2 = X1 + 2X2 + X3 and Y3 = X1 + X2 + 2X3. Then which of the following statements is/are true?

P : The sum of eigenvalues of the variance covariance matrix of (Y1, Y2, Y3) is 18σ2.

Q : The correlation coefficient between Y1 and Y2 equals that between Y2 and Y3.

(A)  P only

(B)  Q only

(C)  Both P and Q

(D)  Neither P nor Q

Answer: (C)

36. Let {Xn}n≥0 be a time-homogeneous discrete time Markov chain with either finite or countable state space S. Then which one of the following statements is true?

(A)  There is at least one recurrent state

(B)  If there is an absorbing state, then there exists at least one stationary distribution

(C)  If all the states are positive recurrent, then there exists a unique stationary distribution

(D)  If {Xn}n≥0 is irreducible, S = {1, 2} and [π1 π2] is a stationary distribution, then  for i = 1, 2

Answer: (B)

37. Let customers arrive at a departmental store according to a Poisson process with rate 10. Further, suppose that each arriving customer is either a male or a female with probability 1/2 each, independent of all other arrivals. Let N(t) denote the total number of customers who have arrived by time t. Then which one of the following statements is NOT true?

(A)  If S2 denotes the time of arrival of the second female customer, then   

(B)  If M(t) denotes the number of male customers who have arrived by time t, then  

(C)  E [(N(t))2] = 100t2 + 10t

(D)  E[N(t)N(2t)] = 200t2 + 10t

Answer: (B)

38. Let X(1) < X(2) < X(3) < X(4) < X(5)be the order statistics corresponding to a random sample of size 5 from a uniform distribution on [0, θ], where θ ∈ (0, ∞). Then which of the following statements is/are true?

P : 3X(2) is an unbiased estimator of θ.

Q : The variance of E[2X(3) | X(5)] is less than or equal to the variance of 2X(3).

(A)  P only

(B)  Q only

(C)  Both P and Q

(D)  Neither P nor Q

Answer: (C)

39. Let X1, X2, … , Xn be a random sample of size n (≥ 2) from a distribution having the probability density function

where θ ∈ (0, ∞). Let X(1) = min{ X1, X2, … , Xn} and  Then E(X(1)| T ) equals

(A)  T/n2

(B)  T/n

(C)   

(D)   

Answer: (A)

40. Let X1, X2, … , Xn be a random sample of size n (≥ 2) from a uniform distribution on [−θ, θ], where θ ∈ (0, ∞). Let X(1) = min{X1, X2, … , Xn} and X(n) = max{X1, X2, … ,Xn}. Then which of the following statements is/are true?

P : (X(1), X(n)) is a complete statistic.

Q : X(n) − X(1) is an ancillary statistic.

(A)  P only

(B)  Q only

(C)  Both P and Q

(D)  Neither P nor Q

Answer: (D)

41. Let {Xn}n≥1 be a sequence of independent and identically distributed random variables having common distribution function F(⋅). Let a < b be two real numbers such that F(x) = 0 for all x ≤ a, 0 < F(x) < 1 for all a < x < b and F(x) = 1 for all x ≥ b. Let Sn(x) be the empirical distribution function at x based on X1, X2, … ,Xn, n ≥ 1. Then which one of the following statements is NOT true?

(A)    

(B)  For fixed x ∈ (a, b) and t ∈ (− ∞, ∞),  where Z is the standard normal random variable

(C)  The covariance between Sn(x) and Sn(y) equals  for all n ≥ 2 and for fixed −∞ < x, y < ∞

(D)  If  then {4n Yn}n≥1 converges in distribution to a central chi-square random variable with 2 degrees of freedom

Answer: (C)

42. Let the joint distribution of random variables X1,X2,X3 and X4 be  where

Then which one of the following statements is true?

(A)   follows a central chi-square distribution with 2 degrees of freedom

(B)   follows a central chi-square distribution with 2 degrees of freedom

(C)   is NOT finite

(D)   is NOT finite

Answer: (D)

43. Let  distribution, where I8 is the 8 × 8 identity matrix. Let  be independent and follow central chi-square distributions with 3 and 4 degrees of freedom, respectively, where Σ1 and Σ2 are 8 × 8 matrices and  denotes transpose of  Then which of the following statements is/are true?

P : Σ1 and Σ2 are idempotent.

Q : Σ1Σ2 = 0, where 0 is the 8 × 8 zero matrix.

(A)  P only

(B)  Q only

(C)  Both P and Q

(D)  Neither P nor Q

Answer: (C)

Q.44 – Q.55 Numerical Answer Type (NAT), carry TWO mark each (no negative marks).

44. Let (X, Y) have a bivariate normal distribution with the joint probability density function

Then 8 E(XY) equals ________

Answer: (3 to 3)

45. Let f: ℝ × ℝ → ℝ be defined by f(x, y) = 8x2 − 2y, where ℝ denotes the set of all real numbers. If M and m denote the maximum and minimum values of f, respectively, on the set {(x, y) ∈ ℝ × ℝ ∶ x2 + y2 = 1}, then M − m equals ________ (round off to 2 decimal places).

Answer: (10.10 to 10.15)

46. Let A = [a u1 u2 u3], B = [b u1 u2 u3] and C = [u2 u3 u1 a + b] be three 4 × 4 real matrices, where a, b, u1, u2 and u3 are 4 × 1 real column vectors. Let det(A), det(B) and det(C) denote the determinants of the matrices A, B and C, respectively. If det(A) = 6 and det(B) = 2, then det(A + B) − det(C) equals _________

Answer: (72 to 72)

47. Let X be a random variable having the moment generating function 

Then P(X > 1) equals __________ (round off to 2 decimal places).

Answer: (0.60 to 0.66)

48. Let {Xn}n≥1 be a sequence of independent and identically distributed random variables each having uniform distribution on [0, 3]. Let Y be a random variable, independent of {Xn}n≥1, having probability mass function

Then P(max{X1,X2, … ,XY} ≤ 1) equals __________ (round off to 2 decimal places).

Answer: (0.20 to 0.26)

49. Let {Xn}n≥1 be a sequence of independent and identically distributed random variables each having probability density function

Let X(n) = max{X1,X2, … ,Xn} for n ≥ 1. If Z is the random variable to which {X(n) − loge n}n≥1converges in distribution, as n → ∞, then the median of Z equals __________ (round off to 2 decimal places).

Answer: (0.32 to 0.42)

50. Consider an amusement park where visitors are arriving according to a Poisson process with rate 1. Upon arrival, a visitor spends a random amount of time in the park and then departs. The time spent by the visitors are independent of one another, as well as of the arrival process, and have common probability density function

If at a given time point, there are 10 visitors in the park and p is the probability that there will be exactly two more arrivals before the next departure, then 1/p equals ________

Answer: (143 to 143)

51. Let {0. 90, 0. 50, 0. 01, 0. 95} be a realization of a random sample of size 4 from the probability density function

where 0. 5 ≤ θ < 1. Then the maximum likelihood estimate of θ based on the observed sample equals __________ (round off to 2 decimal places).

Answer: (0.50 to 0.50)

52. Let a random sample of size 100 from a normal population with unknown mean μ and variance 9 give the sample mean 5. 608. Let Φ(⋅) denote the distribution function of the standard normal random variable. If Φ(1. 96) = 0. 975, Φ(1. 64) = 0. 95 and the uniformly most powerful unbiased test based on sample mean is used to test H0: μ = 5. 02 against H1: μ ≠ 5. 02, then the p-value equals __________ (round off to 3 decimal places).

Answer: (0.045 to 0.055)

53. Let X be a discrete random variable with probability mass function p ∈ {p0, p1}, where

To test H0: p = p0 against H1: p = p1, the power of the most powerful test of size 0. 05, based on X, equals __________ (round off to 2 decimal places).

Answer: (0.20 to 0.22)

54. Let X1, X2, … , X10 be a random sample from a probability density function fθ(x) = f(x − θ), −∞ < x < ∞, where −∞ < θ < ∞ and f(−x) = f(x) for −∞ < x < ∞. For testing H0: θ = 1. 2 against H1: θ ≠ 1. 2, let T+ denote the Wilcoxson Signed-rank test statistic. If η denotes the probability of the event {T+ < 50} under H0, then 32 η equals __________ (round off to 2 decimal places).

Answer: (31.60 to 31.80)

55. Consider the multiple linear regression model Yi = β0 + β1x1,i + β2x2,i + ⋯ + β22x22,i + ϵi, i = 1, 2, … , 123, where, for j = 0, 1, 2, … , 22, βj’s are unknown parameters and ϵi’s are independent and identically distributed N(0, σ2), σ > 0, random variables.

If the sum of squares due to regression is 338. 92, the total sum of squares is 522. 30 and R2adj denotes the value of adjusted R2 then 100 R2adj, equals __________ (round off to 2 decimal places).

Answer: (57.00 to 57.40)

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