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All questions of Practice Test for IIT Jam Mathematics for Mathematics Exam

A group (G, *) has 10 elements. The minimum number of elements of G, which are their own inverse is
  • a)
    2
  • b)
    1
  • c)
    9
  • d)
    0
Correct answer is option 'B'. Can you explain this answer?

Chirag Verma answered
Since,in a group there must be an identity element.Also it is its own inverse. Therefore,minimum number of elements of G,which are their own inverse=1

Find the number of element of order 10 in Z30
    Correct answer is '4'. Can you explain this answer?

    Chirag Verma answered
    Since, the number of elements of order cl in a cyclic group of order n is φ(d), where d is positive divisor of n. Hence, the number of elements of order 10 in  is

    ___________ is the order of {3} in the multiplicative group of integers modulo 5.
      Correct answer is '4'. Can you explain this answer?

      Chirag Verma answered
      The identity of the multiplicative group of integers modulo 5 is {1}. 
      Here
      {3}.5{3} = 4 * {1} [•, 3.3 0 4 (mod 5)]
      ∴ {3}.5{3}.5{3} = {4}.5{3} = {2} * {1} [∵, 4.30 2 (mod 5)]
      ∴{3}.5{3}.5{3}.5{3} = {2}.5{3} = {1} [∵, 2.30 (mod 5)]
      Hence, the order of {3} is 4.

      Find the directional derivative of  φ = x2yz + 4xz2 at (1, - 2 , - 1 ) in the direction 2i - j - 2k.
        Correct answer is '12.34'. Can you explain this answer?

        Chirag Verma answered
        The unit vector in the direction of 2i - j - 2k is
        Then the required directional derivative is
        Since this is positive,increasing in this direction.

        Which of the following is correct?
        • a)
          Every subgroup of an abelian group is normal
        • b)
          Every subgroup of a cyclic group is normal
        • c)
          Intersection of any two normal subgroup is a normal subgroup
        • d)
          If N is a normal subgroup of G and H is any subgroup of G then NH is normal subgroup of G.
        Correct answer is option 'A,B,C'. Can you explain this answer?

        Chirag Verma answered
        Every subgroup of an abelian group is normal as for every x ∈ G and h ∈ H
        Every subgroup of cyclic group is normal and intersection of two normal subgroups is normal subgroup again.
        If N is a normal subgroup of G and H is any subgroup of G then NH is a subgroup of G but NH is necessarily not normal.

        If G be an one empty set
        (1) a(bc) = (ab)c for all a, b, c ∈ G
        (2) For any a, b ∈ G, the equations ax = b and ya = b have solutions in G. 
        then
        • a)
          <G, •> is not group
        • b)
          <G. •> is a group
        • c)
          <G,•> is a sub group
        • d)
          <G, •> is not a sub group.
        Correct answer is option 'B'. Can you explain this answer?

        Mister Genius answered
        Let (1) and (2) hold. To show G is a group, we need prove existence of identity and
        Let a ∈ G be any element inverse.
        By (2) the equations ax = a
        ya = a
        have solutions in G.
        Let x = e and y = f be the solutions.
         ae = a
        fa = a
        Let now b e G be any element then again by (2) some x, y in G s.t.,
        ax = b
        ya = b.
        Now ax = b ⇒ f.(a.x) = f.b
        ⇒ (f.a).x = f.b
        ⇒ a.x = f.b
        ⇒ b = f.b
        Again y.a = h
        ⇒ (y.a).e = b.e
        ⇒y.(a.e) = b.e
        ⇒ y.a = be
        ⇒ b = be
        thus we have b = fb ... (i)
        b = be ... (ii)
        for any b ∈ G
        Putting b = e in (i) and b = f in (ii) we get
        e = fe
        f = fe
        ⇒ e = f.
        Hence ae = a = fa = ea
        i.e., e ∈ G, s.t., ae = ea = a
        ⇒ e is identity.
        Again, for any a ∈ G, and (the identity) e ∈ G, the equations ax = e and ya = e have solutions.
        Let the solutions be x = a1, and y = a2
        then aa1 = e,
        a2a = e
        Now a1 = ea1 = (a2a)a1 = a2(aa1) = a2e = a2.
        Hence aa1 = e = a1a for any a ∈ G
        i.e., for any a ∈ G, some a1 ∈ G satisfying the above relations ⇒ a has an inverse. Thus each element has inverse and, by definition, G forms a group.

        Let G be a group of order 143, then the centre of G is isomorphic to
        • a)
          Z
        • b)
          Z11
        • c)
          Z13
        • d)
          Z143
        Correct answer is option 'D'. Can you explain this answer?

        Chirag Verma answered
        O(G) = 143
        i.e. O(G) =11 x 13 (p < q)
        Here.O(G) = pq , p < q and p X q -1, so G be a cyclic group of order 143 and every cyclic group is an abelian group.
        Hence G is an abelian group, if G be an abelian group then centre of G is equal to group G.
        G = Z(G) [∵ G is an abelian]
        i.e. O[Z(G)] = 143 so Z(G) is isomorphic to Z143.

        Let GL(2, Z5) is a group for multiplication of matrix operation such that ad - be ≠ 0 then order of the group GL(2,Z5) is
          Correct answer is '480'. Can you explain this answer?

          Chirag Verma answered
          We know that the order of general linear group GL(n, Zp) is
          = (Pn-1) (Pn - P) (Pn - P2)_____ (Pn - Pn-1)
          Here P = 5 , n = 2 
          0[GL(2,Z5)] = (52 - 1) (52 - 5)
          = 24 x 20 
          = 480

          Which of the following is a 2 -dimensional subspace of R3 over R ?
          • a)
          • b)
          • c)
          • d)
          Correct answer is option 'D'. Can you explain this answer?

          Chirag Verma answered
          Here (a) be a subspace but basis of it is {(0. 1, 0)} so it be a subspace of dimension 1.
          (b), (c) are not subspace, so they don't have dim.
          Now (d) be a subspace and its basis is {(0, 0. 1) (0, 1. 0)} so it be a subspace with dimension 2.

          Which one of the following is a group?
          • a)
            (N, *) where a * b = a for all a, b ∈ N
          • b)
            (Z, *) where a + b = a - b for all a, b ∈ Z
          • c)
            (Q, *) where a * b = ab/2 for all a, b ∈ Q
          • d)
            (R, *) where a + b = a + b + 1 for all a, b ∈ R
          Correct answer is option 'D'. Can you explain this answer?

          Chirag Verma answered
          (N, *) where 
          closure property a* b = a ∈ N
          Associativity (a * b) * c = a * c = a
          a * (b * c) = a * b = a
          a * (b * c) = a * b = a
          identity
          a * e = a
          a = a
          ⇒ there does not exist identity
          ⇒ (N, *) is not a group.
          (B) (Z, *) where a * b = a - b for all a, b ∈Z (Z, *) is a group if all four properties of the group are satisfied. These properties are
          (1) Closure property : If a, b ∈ Z, then a * b = a - b∈Z => closure property is satisfied
          (2) Associativity => If a, b, c ∈ Z, then (a * b) * c = (a - b) * c = a - b - c ...(i)
          and a*(b*c) = a * ( b - c ) = a - ( b - c ) = a - b + c ...(ii)
          Hence by Eqs. (i) and (ii) (a * b) * c≠a*(b*c)
          Hence the property of associativity is not satisfied.
          => (Z, *) is not a group.
          (C) (Q, *) where  for all a, b ∈ Q. This is not a group since inverse of element 0 ∈ Q does not exist.
          For; identity => let identity is e, then a * e = a, let a ≠ o .
          ⇒ if a ≠ 0 then e = 2, Thus if a = 0 then e cannot be 2
          ⇒ inverse of a = 0 does not exist. Hence it is not a group
          (D) (R, *) w here a * b = a + b + 1 ,a , b ∈ R This is a g roup with identity given as a *
          e = a + e +1 = a
          ⇒ a + e + 1 = a
          ⇒ e + 1 = a - a
          ⇒ e + 1 =0
          ⇒ e = - 1
          Since - 1 ∈ Q, so e ∈ Q, So (R, *) is a group with identity - 1 .

          The area between the curves y = xex and y = xe-x and the line x = 1 is __________ ( Write upto Four decimal Places)
          Correct answer is '0.7357'. Can you explain this answer?

          Chirag Verma answered
          The line x = 1 meets the curves in (1,e) and B(1, 1/e). The second curve is lower cuive as ordinate of B is less than ordinate of A.
          Both the curves pass through origin.
           
          = 0.7357

          How many numbers satisfied the equation x ≌ 7 (mod 17), where x in the range 1 < x < 100.
          • a)
            4
          • b)
            5
          • c)
            6
          • d)
            7
          Correct answer is option 'C'. Can you explain this answer?

          The equation x ≡ 7 (mod 17) can be rewritten as x = 17k + 7, where k is an integer.

          To find the range of x, we can substitute the given range 1 ≤ x ≤ 100 into the equation:

          1 ≤ 17k + 7 ≤ 100
          Subtracting 7 from all parts of the inequality:
          -6 ≤ 17k ≤ 93
          Dividing by 17:
          -6/17 ≤ k ≤ 93/17
          Since k must be an integer, we can round down the lower bound and round up the upper bound:
          -1 ≤ k ≤ 5

          Now we can find the number of values of x within this range:
          For k = -1, we have x = 17(-1) + 7 = 0, which is not within the given range.
          For k = 0, we have x = 17(0) + 7 = 7.
          For k = 1, we have x = 17(1) + 7 = 24.
          For k = 2, we have x = 17(2) + 7 = 41.
          For k = 3, we have x = 17(3) + 7 = 58.
          For k = 4, we have x = 17(4) + 7 = 75.
          For k = 5, we have x = 17(5) + 7 = 92.

          Therefore, there are 6 numbers (7, 24, 41, 58, 75, 92) that satisfy the equation x ≡ 7 (mod 17) within the given range 1 ≤ x ≤ 100.

          If f(x) = (x2 - 1) |x2 - 3x + 2| + cos|x| then the set of point of non-differentiability is,
          • a)
            {1,0,2}
          • b)
            {1,2}
          • c)
            {2}
          • d)
            {0,2}
          Correct answer is option 'C'. Can you explain this answer?

          Point of Non-Differentiability for f(x) = (x^2 - 1) |x^2 - 3x + 2| + cos|x|
          - Finding the Points of Non-Differentiability
          To find the points of non-differentiability for the given function f(x), we need to consider the points where the function is not differentiable.
          - Breakdown of the Function
          The given function f(x) consists of three parts:
          1. (x^2 - 1)
          2. |x^2 - 3x + 2|
          3. cos|x|
          - Examining Each Part
          1. The function (x^2 - 1) is a polynomial function and is differentiable for all real numbers.
          2. The absolute value function |x^2 - 3x + 2| will change its behavior at the roots of the expression inside the absolute value.
          Solving x^2 - 3x + 2 = 0 gives x = 1 and x = 2. Therefore, the function is non-differentiable at x = 1 and x = 2.
          3. The cosine function cos|x| is continuous and differentiable for all real numbers.
          - Conclusion
          Therefore, the points of non-differentiability for the function f(x) = (x^2 - 1) |x^2 - 3x + 2| + cos|x| are x = 1 and x = 2. Hence, the correct answer is option 'c) {2}'.

          If G is a group, Z its center and if G/Z is cyclic then G
          • a)
            must be abelian
          • b)
            must be non abelian
          • c)
            must be normal subgroup
          • d)
            must be subgroup
          Correct answer is option 'A'. Can you explain this answer?

          Chirag Verma answered
          We have given that G/Z is a cyclic group, so let Zg is a generator of the cyclic group G/Z, where g ∈ G.
          W e now show that G is an abelian group i.e.,
          Since a ∈ G, so Za ∈ G/Z. But G/Z is a cyclic group which is gen era ted by Zg. Thus there exists an integer m such that
          Za = (Zg)m = Zgm [∵ Z is a normal subgroup of G]
          Again 
          a ∈ Za and Za = Zgm ⇒ a ∈ Z gm.
          Now
          a ∈ Z g m ⇒ z1 ∈ Z such that a ∈ z1 gm
          Similarly, for b ∈ G, b = zgn, where z2 ∈  z and n is any integer.
          Now
          Again

          Total number of non abelian groups of order 23 . 34. 5 is __________.
            Correct answer is '15'. Can you explain this answer?

            Vivek Kumar answered
            Partitions of 3 are three namely 
            3 = 3,2 + 1, 1 +1 +1.
            Partition of 4 are five namely 
            4 = 4, 3 + 1, 2 + 2, 2 + 1 +1, 1 +1 +1 +1. 
            Partition of 1 is only one 1 = 1 
            Thus there are (I) non isomorphic abelian group of order 2. 
            (II) five non isomorphic abelian group of order 34. and 
            (III) One abelian group of order 5.
            Hence total number of non abelian group of order
            23. 34. 5 = 3 x 5 x 1 = 1 
            =15

            Let G be a group of 35 elements. Then the largest possible size of a subgroup of G other than G itself is ______.
            Correct answer is '7'. Can you explain this answer?

            Chirag Verma answered
            Group G has 35 elements, i.e. its order is 35
            So, possible subgroup sizes can be 1, 5, 7, 35.
            Thus the largest possible size of subgroup other than G itself (proper subgroup) is 7.

            Find the total number of cyclic subgroups of order 10 in
              Correct answer is '6'. Can you explain this answer?

              Veda Institute answered
              Case - I
              |a|= 10 and|b| = 1 or 5. since z100 has a unique cyclic subgroup of order 10 and cyclic group of order 10 has four generators, i.e. there are four choices for a Similarly, there are five choices for b. This gives 20 possibilities for (a,b).
              Case - II lal = 2 and|b| = 5 .
              Since any finite cyclic group of even order has a unique subgroup of order 2, there is only one choice for a.
              So, obviously there are four choices for b.
              Hence  has 24 elements of order 10. Because each cyclic subgroup of order 10 has four elements of order 10 and no two of the cyclic subgroups can have an element of order 10 in common. There must be 24/4 = 6 cyclic subgroups of order 10.

              Let T = { z ∈ c : | z | = 1} then (T, x) is a group which o f the following are not subgroup of (T, x)
              • a)
                ({1, -1, i, -i}, x)
              • b)
                ({1.-1}. X)
              • c)
              • d)
                None of these
              Correct answer is option 'D'. Can you explain this answer?

              Mister Genius answered
              If T = {z ∈ s c : | z | = 1} then (T, x) is said to be a circle group All though the circle group has infinite order it has many finite subgroups as the complex numbers satisfying the equation zn = 1 are called the nth root of unity. They are

              Number of generators of group Z16
              • a)
                7
              • b)
                8
              • c)
                9
              • d)
                16
              Correct answer is option 'B'. Can you explain this answer?

              Chirag Verma answered
              Since Z16 = {0, 1 , 2 ..... . 15}
              The numbers 1, 3, 5, 7, 9, 11, 13,15 are the elements of Z16 that are relatively prime to 16. Each of these elements generates Z16.
              So no. of generators = 8

              Solution of the differential equation 
              • a)
                y2 = c1x
              • b)
                y2 = c1 x2+c2x3
              • c)
                y2 = c2x2+2c1x
              • d)
                y2= x(c2,x - 2c1)
              Correct answer is option 'D'. Can you explain this answer?

              Chirag Verma answered
              The given equation can be re-written as 
              Integrating 
              Putting y2 = v so that 2y (dy/dx) = (dv/dx). We then get
              which is linear. Its I.F = 

              The total number of elements of order 5 in  _____.
                Correct answer is ''. Can you explain this answer?

                Vivek Kumar answered
                Here we count the number of elements (a,b) in  with the property that

                clearly this requires that either |a| = 5 and |b| = 1 or 5 or |b| = 5 and |a|=1 or 5. Here, we consider three mutually exclusive cases.
                Case-I |a| = 5 and.|b| = 5 .Here there are four choices for a(5.10,15.20) and four choices for b. This gives 16 elements of order 5.
                Case-ll |a| = 5 and |b| = 1 ,So there are four choices for a and only one for b.
                This gives four more elements of order 5.
                Case-Ill a| = 1 and |b| = 5. here only one choice for a and four choices for b. so we obtain four more elements of order 5.
                Hence  has 24 elem ents of order 5.

                Changing the order of the integration  gives
                • a)
                • b)
                • c)
                • d)
                Correct answer is option 'C'. Can you explain this answer?

                Chirag Verma answered
                Here the integration extends to all points of the space bounded by parabola y = 1 - x2 and circle 
                The given integral breaks up in two integrals : first corresponding to the area ABCO and second to the area AOCD.
                Now solving y = 1 - x2 for x, we have 
                Clearly upper and lower limit o f x for the area OABC are  and for area AOCD upper and lower limits of x is  and limits of y is O to -1
                Hence, we have

                How many generators are exists for the cyclic group of order 26.
                  Correct answer is '12'. Can you explain this answer?

                  Chirag Verma answered
                  Let G = [ a ] be a cyclic group . then generators of this group is of the from am
                  where m < 26 . [ Co-prime of 26 ]
                  Hence m = 1, 3 ,5 , 7 , 9 , 1 1 , 15 ,17 ,1 9,2 1 ,23 ,25 total generators are 12.

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