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Published on: 02/11/2019
Discrete Mathematics
Download Tamil Nadu 12th Standard Maths question papers, model tests, one-mark questions, important questions, and public exam papers in PDF format. Free study materials and answer keys for TN State Board students.
Questions + Answers key
Take MCQ Maths Test1.
Write the converse, inverse, and contrapositive of each of the following implication.
If x and y are numbers such that x = y, then x2 = y2
2.
Fill in the following table so that the binary operation ∗ on A = {a, b, c} is commutative.
| * | a | b | c |
| a | b | ||
| b | c | b | a |
| c | a | c |
3.
Determine the truth value of each of the following statements
(i) If 6 + 2 = 5 , then the milk is white.
(ii) China is in Europe or \(\sqrt3\) is an integer
(iii) It is not true that 5 + 5 = 9 or Earth is a planet
(iv) 11 is a prime number and all the sides of a rectangle are equal
4.
Let p: Jupiter is a planet and q: India is an island be any two simple statements. Give verbal sentence describing each of the following statements.
(i) ¬p
(ii) p ∧ ¬q
(iii) ¬p ∨ q
(iv) p➝ ¬q
(v) p↔q
5.
Let A =\(\begin{bmatrix} 0 & 1 \\ 1 & 1 \end{bmatrix},B=\begin{bmatrix} 1 & 1 \\ 0 & 1 \end{bmatrix}\)be any two boolean matrices of the same type. Find AvB and A\(\wedge\)B.
6.
Examine the binary operation (closure property) of the following operations on the respective sets (if it is not, make it binary)
\(a*b=\left( \frac { a-1 }{ b-1 } \right) ,\forall a,b\in Q\)
7.
Examine the binary operation (closure property) of the following operations on the respective sets (if it is not, make it binary)
a*b = a + 3ab − 5b2; ∀a,b∈Z
8.
Prove p⟶(q⟶r) ☰ (p ∧ q)⟶r without using truth table.
9.
Using truth table check whether the statements ¬(p V q) V (¬p ∧ q) and ¬p are logically equivalent.
10.
Show that p ➝ q and q ➝ p are not equivalent
11.
Verify whether the following compound propositions are tautologies or contradictions or contingency
((p⟶ q) ∧ (q ⟶ r)) ⟶ (p ⟶ r)
12.
Verify whether the following compound propositions are tautologies or contradictions or contingency
( p ⟶ q) ↔️ (~ p ⟶ q)
13.
Verify whether the following compound propositions are tautologies or contradictions or contingency
(( p V q)∧ ¬ p) ➝ q
14.
Verify whether the following compound propositions are tautologies or contradictions or contingency
(p ∧ q) ∧ ¬ (p ∨ q)
15.
Verify the
(i) closure property,
(ii) commutative property,
(iii) associative property
(iv) existence of identity and
(v) existence of inverse for the arithmetic operation + on Z.
16.
Prove that q ➝ p ≡ ¬p ➝ ¬q
17.
Show that ¬( p ∧ q) ≡ ¬p V ¬q
18.
Construct the truth table for the following statements.
(¬p ⟶ r) ∧ ( p ↔️ q)
19.
Construct the truth table for the following statements.
( p V q) V ¬q
20.
Construct the truth table for the following statements.
¬(p ∧ ¬q)
1.
If x and y are numbers such that x = y, then x2 = y2
Converse statement :
If x and y are numbers such that x2 = y2 then x = y
Inverse statement :
If x and y are numbers such that x ≠ y then x2 ≠ y2
Contrapositive statement :
If x and y are numbers such that x2≠ y2 then x ≠ y
2.
Given * on A is commutative
Given b * a = c ⇒ a * b = c
Given c * a = a ⇒ a * c = a
Given b * c = a ⇒ c * b = a
Hence
| * | a | b | c |
| a | b | c | a |
| b | c | b | a |
| c | a | a | c |
3.
(i) If 6 + 2 = 5, then the milk is white.
Let p: 6 + 2 = 5 (F)
q: Milk is white (T)
p ➝ q is having the truth value T
(ii) China is in Europe or \(\sqrt3\) is an integer.
p: China is in Europe (F)
q: \(\sqrt3\) is an integer (F)
p v q is having the truth value (F).
(iii) It is not true time 5 + 5 = 9 or Earth is a planet.
Let P: 5 + 5 = 9 is not true (T)
q: Earth is a planet (T
~p ∨ q is having the truth value T
(iv) 11 is a prime number and all the sides of a rectangle are equal.
p:11 is a prime number (T)
q: Allthe sides of arectangle areequal (F)
p ^ q is having the truth value F
4.
Given p : Jupiter is a planet and
q : India is an island.
(i) ¬p : Jupiter is not a planet.
(ii) p ∧ ¬q : Jupiter is a planet and India is not an island.
(iii) ¬p ∨ q : Jupiter is not a planet or India is an island.
(iv) p➝ ¬q : If Jupiter is a planet then India is not an island.
(v) p↔q : Jupiter is a planet if and only if India is an island.
5.
Then A∨ B =\(\begin{bmatrix} 0 & 1 \\ 1 & 1 \end{bmatrix}\vee \begin{bmatrix} 1 & 1 \\ 0 & 1 \end{bmatrix}=\begin{bmatrix} 0\vee 1 & 1\vee 1 \\ 1\vee 0 & 1\vee 1 \end{bmatrix}=\begin{bmatrix} 1 & 1 \\ 1 & 1 \end{bmatrix}\)
\(A\wedge B=\begin{bmatrix} 0 & 1 \\ 1 & 1 \end{bmatrix}\wedge \begin{bmatrix} 1 & 1 \\ 0 & 1 \end{bmatrix}=\begin{bmatrix} 0\wedge 1 & 1\wedge 1 \\ 1\wedge 0 & 1\wedge 1 \end{bmatrix}=\begin{bmatrix} 0 & 1 \\ 0 & 1 \end{bmatrix}\)
6.
In this problem a ∗ b is in the quotient form. Since the division by 0 is undefined, the denominator b -1 must be nonzero.
It is clear that b −1 = 0 if b = 1. As 1∈Q, ∗ is not a binary operation on the whole of Q. However it can be found that by omitting 1 from Q, the output a ∗b exists in Q\{1}. Hence ∗ is a binary operation on Q\{1}.
7.
Since × is binary operation on Z, a,b ∈ Z⇒ a × b = ab∈Z and b × b = b2∈Z ...(1)
The fact that + is binary operation on Z and (1) ⇒ 3ab = (ab + ab + ab) ∈Z and 5b2= (b2+b2+b2+b2+b2)∈Z ...(2)
Also a∈Z and 3ab ∈Z implies a+3ab∈Z ...(3)
(2),(3), the closure property of -on Z yield a * b = (a+3ab-5b2)∈Z. Since a * b belongs to Z, * is a binary operation on Z.
8.
Prove that p⟶(q⟶r) = (p ∧ q)⟶r without using truth table. From example we know that p⟶ q = ~p V q
Consider LHS = p⟶(q⟶r)
= p ⟶ (~q V r) [Implication Law]
= ~p V (~q V r) [Implication Law]
= (~p V ~q) V r [associative property]
= ~(p ∧ q) V r [using Demorgan's law]
= (p ∧ q) ⟶ r [Implication Law]
Hence proved.
9.
~(p V q) V (~p ∧ q) and ~p
| p | q | p V q | ~(p ∧ q) | ~p | ~p ∧ q | ~(p V q) V (~p ∧ q) |
| T | T | T | F | F | F | F |
| T | F | T | F | F | F | F |
| F | T | T | F | T | T | T |
| F | F | F | T | T | F | T |
The entries in column (5) and column (7) are identical.
∴ ~(p V q) V (~p ∧ q) and ~p are logically equivalent.
10.
| p | q | p ➝ q | q ➝ p |
| T | T | T | T |
| T | F | F | T |
| F | T | T | F |
| F | F | T | T |
The entries in column (3) and column (4) are not identical.
11.
| p | q | r | q ⟶ r | p⟶ q | q ⟶ r | (p⟶ q) ∧ (q ⟶ r) | ((p⟶ q) ∧ (q ⟶ r)) ⟶ (p ⟶ r) |
| T | T | T | T | T | T | T | T |
| T | T | F | F | T | F | F | T |
| T | F | T | T | F | T | F | T |
| T | F | F | F | F | T | F | T |
| F | T | T | T | T | T | F | T |
| F | T | F | T | T | F | F | T |
| F | F | T | T | T | T | T | T |
| F | F | F | T | T | T | T | T |
∴ ((p⟶ q) ∧ (q ⟶ r)) ⟶ (p ⟶ r)
The given statement is a tautology.
12.
| p | q | p ⟶ q | ~p | ~p ⟶ q | ( p ⟶ q) ↔️ (~p ⟶ q) |
| T | T | T | F | T | T |
| T | F | F | F | T | F |
| F | T | T | T | T | T |
| F | F | T | T | F | F |
Since this is neither a tautology not a contradiction
( p ⟶ q) ↔️ (~p ⟶ q) is a contingency.
13.
(( p V q)∧ ~p)) ➝ q
| p | q | p V q | ~p | ( p V q) ∧ ~q | ( p V q) ∧ ~q |
| T | T | T | F | F | T |
| T | F | T | F | F | T |
| F | T | T | T | T | T |
| F | F | F | T | F | T |
The statement (( p V q)∧ ~p) ➝ q is a tautology.
14.
| p | q | p ∧ q | p ∨ q | ~p ∨ q | (p ∧ q) ∧ ~(p ∨ q) |
| T | T | T | T | F | F |
| T | F | F | T | F | F |
| F | T | F | T | F | F |
| F | F | F | F | T | F |
The statement (p ∧ q) ∧ ~(p ∨ q)
15.
(i) m + n∈Z, ∀m, n∈Z. Hence + is a binary operation on Z.
(ii) Also m + n = n + m,∀m, n∈Z. So the commutative property is satisfied
(iii) ∀m, n, p∈Z, m+ (n + p) = (m+ n) + p. Hence the associative property is satisfied.
(iv) m + e = e + m = m ⇒ e = 0. Thus ヨ 0∈Z⋺(m+ 0) = (0 + m) = m. Hence the existence of identity is assured.
(v) m + m' = m'+ m = 0 ⇒ m' = −m. Thus ∀∈Z,ョ−m∈Z ⋺ m+ (−m) = (−m) + m = 0. Hence, the existence of inverse property is also assured. Thus we see that the usual addition + on Z satisfies all the above five properties.
16.
| p | q | q ➝ p | ~p | ~q | ~q ➝ ~p |
| T | T | T | F | F | T |
| T | F | T | F | T | T |
| F | T | F | T | F | F |
| F | F | T | T | T | T |
The entries in the columns corresponding q ➝ p and ~p ➝ ~q are identical and hence they are equivalent.
q ➝ p ≡ ~p ➝ ~q
Hence proved
17.
~( p ∧ q) ≡ ~p V ~q
| p | q | p ∧ q | ~(p ∧ q) | ~p | ~p | ~p V ~q |
| T | T | T | F | F | F | F |
| T | F | F | T | F | T | T |
| F | T | F | T | T | F | T |
| F | F | F | T | T | T | T |
From column (4) and column (7), the entries are Identical.
ஃ ~( p ∧ q) ≡ ~p V ~q are identical and hence they are equivalent.
18.
Truth Table for (~p ⟶ r) ∧ ( p ↔️ q)
| p | q | r | ~ p | ~ p ⟶ r | p ↔️ q | (~p ⟶ r) ∧ ( p ↔️ q) |
| T | T | T | F | T | T | T |
| T | T | F | F | T | T | T |
| T | F | T | F | T | F | F |
| T | F | F | F | T | F | F |
| F | T | T | T | T | F | F |
| F | T | F | T | F | F | F |
| F | F | T | T | T | T | T |
| F | F | F | T | F | F | F |
19.
Truth Table for ( p V q) ∧ ~q
| p | q | p V q | ~q | ( p V q) ∧ ~q |
| T | T | T | F | T |
| T | F | T | T | T |
| F | T | T | F | T |
| F | F | F | T | T |
20.
Truth Table for ~(p ∧ ~q)
| p | q | ~q | p ∧ ~q | ~(p ∧ ~q) |
| T | T | F | F | T |
| T | F | T | T | F |
| F | T | T | F | T |
| F | F | T | F | T |
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