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Here is the best top 20 NDA Maths questions Objective type which can help to improve in your preparation. Answer Key is also attached in the end.   Question 1. Let * be a binary operation on set Q – {1} defind by a * b = a + b – ab : a, b ∈ Q – {1}. Then * is (a) Commutative(b) Associative(c) Both (a) and (b)(d) None of these Question 2. The binary operation * defined on N by a * b = a + b + ab for all a, b ∈ N is (a) commutative only(b) associative only(c) both commutative and associative(d) none of these Question 3. The number of commutative binary operation that can be defined on a set of 2 elements is (a) 8(b) 6(c) 4(d) 2 Question 4. Let T be the set of all triangles in the Euclidean plane, and let a relation R on T be defined as aRb if a is congruent to b ∀ a, b ∈ T. Then R is (a) reflexive but not transitive(b) transitive but not symmetric(c) equivalence(d) None of these Question 5. The maximum number of equivalence relations on the set A = {1, 2, 3} are (a) 1(b) 2(c) 3 (d) 5 Question 6. Let us define a relation R in R as aRb if a ≥ b. Then R is (a) an equivalence relation(b) reflexive, transitive but not symmetric(c) symmetric, transitive but not reflexive(d) neither transitive nor reflexive but symmetric Question 7. Let A = {1, 2, 3} and consider the relation R = {(1, 1), (2, 2), (3, 3), (1, 2), (2, 3), (1, 3)}. Then R is (a) reflexive but not symmetric(b) reflexive but not transitive(c) symmetric and transitive(d) neither symmetric, nor transitive Question 8. The identity element for the binary operation * defined on Q – {0} as a * b = ab2 ∀ a, b ∈ Q – {0) is (a) 1(b) 0(c) 2(d) None of these Question 9. Let A = {1, 2, 3, …. n} and B = {a, b}. Then the number of surjections from A into B is (a) nP2(b) 2n – 2(c) 2n – 1(d) none of these Question 10. Let f : R → R be defind by f(x) = 1x ∀ x ∈ R. Then f is (a) one-one(b) onto(c) bijective(d) f is not defined Question 11. Which of the following functions from Z into Z are bijective? (a) f(x) = x3(b) f(x) = x + 2(c) f(x) = 2x + 1(d) f(x) = x2 + 1 Question 12. Let f : R → R be the functions defined by f(x) = x3 + 5. Then f-1(x) is (a) (x+5)13(b) (x−5)13(c) (5−x)13(d) 5 – x Question 13. Let f : R – {35} → R be defined by f(x) = 3x+25x−3. Then (a) f-1(x) = f(x)(b) f-1(x) = -f(x)(c) (fof) x = -x(d) f-1(x) = 119 f(x) Question 14. Let f : R → R be given by f(x) = tan x. Then f-1(1) is (a) π4(b) {nπ + π4; n ∈ Z}(c) Does not exist(d) None of these Question 15. Let R be a relation on the set N of natural numbers denoted by nRm ⇔ n is a factor of m (i.e. n | m). Then, R is (a) Reflexive and symmetric(b) Transitive and symmetric(c) Equivalence(d) Reflexive, transitive but not symmetric Question 16. Let S = {1, 2, 3, 4, 5} and let A = S × S. Define the relation R on A as follows:(a, b) R (c, d) iff ad = cb. Then, R is (a) reflexive only(b) Symmetric only(c) Transitive only(d) Equivalence relation Question 17. Let R be the relation “is congruent to” on the set of all triangles in a plane is (a) reflexive(b) symmetric(c) symmetric and reflexive(d) equivalence Question 18. Total number of equivalence relations defined in the set S = {a, b, c} is (a) 5(b) 3!(c) 23(d) 33 Question 19. The relation R is defined on the set of natural numbers as {(a, b) : a = 2b}. Then, R-1 is given by (a) {(2, 1), (4, 2), (6, 3),….}(b) {(1, 2), (2, 4), (3, 6), ……..}(c) R-1 is not defiend(d) None of these Question 20. Let X = {-1, 0, 1}, Y = {0, 2} and a function f : X → Y defiend by y = 2×4, is (a) one-one onto(b) one-one into(c) many-one onto(d) many-one into   TOP 20 NDA MATHS QUESTIONS  Answer Key: – Question No. Answer Question No. Answer Question 1 C Question 11 B Question 2 C Question 12 B Question 3 D Question 13 A Question 4 C Question 14 B Question 5 D Question 15 D Question 6 B Question 16 D Question 7 A Question 17 D Question 8 C Question 18 A Question 9 B Question 19 B Question 10 D Question 20 C