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All questions of Mathematical Reasoning for JEE Exam

In order to prove the statement “p if and only if q” we need to show:
  • a)
    If p is false, then q is false.
  • b)
    If p is true, then q is false
  • c)
    If p is false, then q is true
  • d)
    If p is true, then q is true
Correct answer is option 'D'. Can you explain this answer?

It is necessary to provide evidence or logical reasoning that supports the truth of the statement. This can be done through various means, such as conducting experiments, analyzing data, presenting empirical evidence, or providing logical arguments based on facts and principles. The proof should be objective and verifiable, so that it can be accepted by others as valid and reliable. Additionally, it is important to consider counterarguments and address any potential objections or alternative explanations to strengthen the proof.

A compound statement with an ‘Or’ is false when both the component statements are ……
  • a)
    Same
  • b)
    True
  • c)
    Different
  • d)
    False
Correct answer is option 'D'. Can you explain this answer?

Dinesh Kotha answered
Any compound statement which has And as the connecting word is said to be false if all its component statements are false. A compound statement which has Or as the connecting word is said to be true if one of its component statement orboth the component statements is true.

Let p and q be two propositions. Then the implication p↔∼q is true ,when
  • a)
    p is true and q is true
  • b)
    p is true and q is false
  • c)
    p is false and q is true
  • d)
    both p and q are false
Correct answer is option 'C'. Can you explain this answer?

Notation: Negation is denoted by the symbol ~
Bi-conditional:
Let, p and q are two simple propositions. If p and q both the propositions are either True or False then Bi-conditional gives the output as True otherwise if anyone is False then the output is False.
Notation: Bi-conditional is denoted by the symbol ⇔
Step-2: Truth Table:
The truth table is used to perform logical operations on given propositions. It is used to check whether the given propositional statement is either True or False. Using some of the logical operations like AND, OR, NOR, Conditional, and Bi-conditional.
Given p and q are both simple propositions
The truth table for p⇔~q is given below
pq~qp⇔~q
TT F  F
TFT   T
FTF   T
FFT   F
Where T is True and F is False.
From the above table, we can conclude p⇔~q is True if p is False and q is True.
Hence option 'C' is the correct answer.

There are 25 days in a month. This is
  • a)
    an implication
  • b)
    a quantifier
  • c)
    a compound statement
  • d)
    a statement
Correct answer is option 'D'. Can you explain this answer?

The average menstrual cycle is about 25-30 days, but it can be as short as 21 days or longer than 35 — it's different from person to person. The number of days in your cycle may also vary from month to month. When you get your period, it's normal to bleed anywhere from 2 to 7 days.

The contra positive of a statement p ⇒ q, is the statement
  • a)
    ~q ⇒ ~p
  • b)
    ~ q ⇒ p
  • c)
    q ⇒ p
  • d)
    q⇒ ~ p
Correct answer is option 'A'. Can you explain this answer?

Praveen Kumar answered
Contraceptive of a→b is ∼b→∼a
Then,Contraceptive of p→(∼q→∼r)
≡∼(∼q→∼r)→∼p
≡∼(q∧∼r)→∼p[a→b≡∼a∧b]
≡(∼q∨r)→∼p  [Demorgas law]

For any three propositions p, q, and r, the proposition (p∧q)∧(q∧r) is true, when
  • a)
    p is true and q, r are false
  • b)
    p, q, r are all true
  • c)
    p, q are true and r is false
  • d)
    p, q, r are all false
Correct answer is option 'B'. Can you explain this answer?

Priyanka Basak answered
Q) ∨ (p ∧ r) is logically equivalent to the proposition (p ∨ r) ∧ (q ∨ r).

To show this, we can use a truth table:

| p | q | r | p ∨ q | p ∧ r | (p ∨ q) ∨ (p ∧ r) | (p ∨ r) ∧ (q ∨ r) |
|---|---|---|-------|-------|-------------------|-------------------|
| T | T | T | T | T | T | T |
| T | T | F | T | F | T | T |
| T | F | T | T | T | T | T |
| T | F | F | T | F | T | T |
| F | T | T | T | F | T | T |
| F | T | F | T | F | T | T |
| F | F | T | T | F | F | F |
| F | F | F | F | F | F | F |

As we can see from the truth table, the two propositions have the same truth values for all possible truth values of p, q, and r. Therefore, they are logically equivalent.

Negation of the statement p→(q ∨ r) is
  • a)
    ∼p→∼(q ∨ r)
  • b)
    ∼p→∼(q ∧ r)
  • c)
    (q ∨ r)→ p
  • d)
    p ∧ (∼q ∧∼r )
Correct answer is option 'D'. Can you explain this answer?

The correct option is D p ∧ (∼q ∧∼r)
We know that, ∼(p → q)≡ p ∧ (∼q)
Also, negation of (q ∨ r) is (∼q∧∼r)
So, ∼(p→(q ∨ r))≡ p ∧(∼q∧∼r)

The contrapositive of 2x + 3 = 9 ⇒ x ≠ 4 is
  • a)
    x ≠ 4, 2x+3 ≠ 9
  • b)
    x = 4, 2x+3 ≠ 9
  • c)
    x = 4, 2x+3 = 9
  • d)
    x ≠ 4, 2x+3 = 9
Correct answer is option 'B'. Can you explain this answer?

Bhavana Gupta answered
Explanation:

Contrapositive:
The contrapositive of a statement is formed by negating both the hypothesis and conclusion of the original statement and switching their order.

Given Statement:
2x + 3 = 9 → x ≠ 4

Contrapositive:
x = 4 → 2x + 3 ≠ 9

Explanation:
- The original statement states that if 2x + 3 = 9, then x is not equal to 4.
- The contrapositive of this statement states that if x is equal to 4, then 2x + 3 is not equal to 9.
- Therefore, the correct contrapositive of the given statement is option B: x = 4, 2x + 3 ≠ 9.

Conclusion:
The contrapositive of the given statement is correctly represented in option B.

Which of the following is a proposition ?
  • a)
    Logic is an interesting subject
  • b)
    I am a lion
  • c)
    A half open door is half closed
  • d)
    A triangle is a circle and 10 is a prime number
Correct answer is option 'D'. Can you explain this answer?

Kritika Khanna answered
Proposition in Logic

Definition of Proposition:
A proposition is a statement that is either true or false.

Examples of Statements:
- Logic is an interesting subject.
- I am a lion.
- A half-open door is half closed.
- A triangle is a circle and 10 is a prime number.

Explanation:
Out of the four given statements, only option 'D' is a proposition because it can be evaluated as either true or false. A triangle cannot be a circle and 10 is not a prime number, so the statement is false.

Option 'A' is not a proposition because it is a subjective statement and cannot be evaluated as true or false. It may be interesting to some people and not to others.

Option 'B' is not a proposition because it is a false statement. The speaker is not actually a lion.

Option 'C' is not a proposition because it is an ambiguous statement. The meaning of "half-open" can vary depending on the context, so it cannot be evaluated as true or false.

Therefore, the only proposition in the given options is option 'D'.

Which of the following sentences is a statement ?
  • a)
    2 is the smallest prime number
  • b)
    Aarushi is a pretty girl
  • c)
    What are you doing 
  • d)
    Oh ! It is amazing
Correct answer is option 'A'. Can you explain this answer?

Explanation:

A statement is a declarative sentence that can be either true or false. It gives some information or makes some assertion about the subject. The subject can be a person, place, thing, or idea. Let's analyze the given options to identify which one is a statement.

a) 2 is the smallest prime number - This is a declarative sentence that gives some information about the number 2. It is a statement.

b) Aarushi is a pretty girl - This is also a declarative sentence that makes an assertion about a person named Aarushi. It is a statement.

c) What are you doing? - This is an interrogative sentence that asks a question. It is not a statement.

d) Oh! It is amazing - This is an exclamatory sentence that expresses a strong emotion. It is not a statement.

Therefore, the correct answer is option 'A' - 2 is the smallest prime number, which is a statement.

The contrapositive of (p∨q)→ r is
  • a)
    ∼r→(p∧q)
  • b)
    ∼r→∼(p∨q)
  • c)
    p→(p∧q)
  • d)
    ∼r→(∼p∧∼q)
Correct answer is option 'D'. Can you explain this answer?

Nishanth Gupta answered
Contrapositive of p→q is ∼q→∼p.
∴ Contrapositive of (p∨q)⇒r  is ∼r⇒∼(p∨q) i.e. ∼r⇒(∼p∧∼q).

Logical equivalent proposition to the proposition ∼(p∨q) is
  • a)
    ∼p↔∼q
  • b)
    ∼p∧∼q
  • c)
    ∼p∨∼q
  • d)
    ∼p→∼q
Correct answer is option 'B'. Can you explain this answer?

Nisha Banerjee answered
The logical equivalent proposition to a given proposition depends on the specific proposition in question. Please provide the proposition for which you would like to find the logical equivalent.

The contrapositive of the inverse of p⇒ ~q is
  • a)
    p ⇒ q 
  • b)
    ~q ⇒ ~p 
  • c)
    ~q ⇒ p
  • d)
    ~p ⇒ ~q
Correct answer is option 'C'. Can you explain this answer?

Neha Sharma answered
The inverse of p ⇒ ∼q is ∼p ⇒ q 
The contrapositive of ∼p ⇒ q is ∼q ⇒ p. [∴ Contrapositive of p ⇒ q is∼q ⇒ p.]

Which of the following is logically equivalent to ∼(p↔q) ?
  • a)
    (p∨q)∨(q∧p)
  • b)
    (p∨q)∨(q∧∼p)
  • c)
    (p∨∼q)∨(q∧∼p)
  • d)
    none of these
Correct answer is option 'C'. Can you explain this answer?

Sanaya Patel answered


Logical Equivalence Explanation:

Logical equivalence means two statements have the same truth values in all possible scenarios. In this case, we are looking for a statement that is logically equivalent to ∼(p↔q).

Option Analysis:

a) (p∨q)∨(q∧p)
This statement is not logically equivalent to ∼(p↔q) as it involves both OR and AND operations.

b) (p∨q)∨(q∧¬p)
This statement is not logically equivalent to ∼(p↔q) as it has a negation on p which is not present in the original statement.

c) (p∨¬q)∨(q∧¬p)
This statement is logically equivalent to ∼(p↔q) as it represents the exclusive OR operation. The exclusive OR (XOR) operation is true when the inputs are different, which is the same as the biconditional statement.

d) none of these
This option is incorrect as we have found a logically equivalent statement in option c.

Therefore, the correct answer is option c) (p∨¬q)∨(q∧¬p).

p∧(q∧r) is logically equivalent to
  • a)
    (p∨q)∧r
  • b)
    (p∧q)∧r
  • c)
    p→(q∧r)
  • d)
    (p∨q)∨r
Correct answer is option 'B'. Can you explain this answer?

Maulik Verma answered
There are many words that begin with the letter "p." Here are a few examples:

1. Pizza
2. Penguin
3. Pencil
4. Party
5. Paint
6. Phone
7. Park
8. Puppy
9. Peach
10. Potato

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