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Validating statements - class-XI

Description: validating statements
Number of Questions: 16
Created by:
Tags: mathematical reasoning proofs in mathematics maths
Attempted 0/16 Correct 0 Score 0

"If it is a good watch then it is a Titan watch. It is a Titan watch, therefore, it is a good watch". This argument is _____________.

  1. valid

  2. invalid

  3. may be valid or invalid

  4. invalid if conditional connective is replaced by biconditional connective


Correct Option: A

While simplifying $\sqrt { \frac { 1-cosx }{ 1+cosx }  } $, two students got the following two answers A & B.
A)  cosec x - cot x  (B)   $\frac { 1 }{ cosecx+cotx } $ What can you say about answers ?

  1. Both A & B are worng

  2. Both A & B are right

  3. A is right B is wrong

  4. B is right A is wrong


Correct Option: A
State whether the statement
P: "if x is a real number such that $x^3+2x=0$, then $x$ is $0$"  is true/false
  1. True

  2. False


Correct Option: A

State whether the statement
P: "if x is a real number such that $x^3+2x=0$, then $x$ is $0$" is true/false.

  1. True

  2. False


Correct Option: A

Choose the incorrect statements

  1. Digit at the units place of $3^{51}$ is $9$

  2. If $i-f=(9-\sqrt{82})^{11}$ and $< f < 1 $, then $'i'$ is an even integers

  3. If $7^{80}$ is divided by $13$, then the remainder is $9$

  4. If only $6^{th}$ term in the expression of $\left(\dfrac{x}{5}+\dfrac{2}{5}\right)^{n} $ ahs numerically greatest coefficient, then $n=7$


Correct Option: A

Check the validity of the following statement:
$p:100$ is a multiple of $4$ and $5$

  1. True

  2. False


Correct Option: A
Explanation:

$r:100$ is a multiple of $4\rightarrow$ TRUE $(4\times 25)$


$s:100$ is a multiple of $5\rightarrow$ TRUE $(5\times 20)$

Hence $p$ is true

Determine whether the argument used to check the validity of the following statement is correct.
$p:$ If $x^{2}$ is irrational, then $x$ is rational'
The statement is true because the number $x^{2}=\pi^{2}$ is irrational, therefore $x=\pi$ irrational.

  1. True

  2. False


Correct Option: B
Explanation:

Here, the argument used is,


$x^2=\pi^2$ is irrational, therefore $x=\pi$ is irrational and, $p:$ " If 

$x^2$ is irrational, then $x$ is rational.

Let us take an irrational number given by $x=\sqrt n$,
where $n$ is a rational number.

Now, square both sides, we get,
$x^2=k$

Therefore, $x^2$ is a rational number, which contradicts our statement. 
Hence, the argument used to check validity of given statement is false.

Check the validity of the following statement:
$p:60$ is a multiple of $3$ and $5$

  1. True

  2. False


Correct Option: A
Explanation:
$r:60$ is a multiple of $3\quad (3\times 20)$

$s:60$ is a multiple of $5\quad (5\times 12)$

Hence $p$ is true

State whether the statement
$p:$ If $x$ is a real number such that $x^{3}+19x=0$ , then $x$ is $0$ is true / False

  1. True

  2. False


Correct Option: A
Explanation:

$x^3 + 19x= 0$

$x(x^2 + 19)=0$
$x = 0$,      $x^2 + 19 =0$ 
so given statement is true

Check the validity of the following statement:
$p:125$ is a multiple of $5$ and $7$

  1. True

  2. False


Correct Option: B
Explanation:
$r:125$ is a multiple of $5\rightarrow$ TRUE $(5\times 25)$

$s:125$ is a multiple of $7\rightarrow$ FALSE 

Hence $p$ is false.

Tell if the following statement is true or false. In case give a valid reason for saying so
$p:$ If $x$ and $y$ are integers such that $x>y$. then $-x<-y$.

  1. True

  2. False


Correct Option: A
Explanation:

Given $x>y$


Multiply both sides by $-1$

$-x<-y$ $\therefore$ both statements true.

If p and q are mathematical statements, then in order to show that the statement p and q is true, we need to show that:

  1. The statement p is true and the statement q is not true

  2. The statement p is false and the statement q is true.

  3. The statement p is true and the statement q is false

  4. The statement p is true and the statement q is true


Correct Option: D

The component statements are:

p: You are wet when it rains.

q: You are wet when you are in river.

The compound statement of these component statements using appropriate connective is:

  1. You are not wet when you are in river or it rains.

  2. You are wet when you are in river and it rains.

  3. You are wet when it rains and you are in a river

  4. You are wet when it rains or you are in a river.


Correct Option: D

Two pairs of statement are:
p: If a quadrilateral is a rectangle, then its opposite sides are equal.
q: If opposite sides of a quadrilateral are equal, then the quadrilateral is a rectangle.
The combined statement of these pairs using If and only if is:

  1. A quadrilateral is a rectangle if and only if its all sides are equal.

  2. A quadrilateral is a rectangle if and only if its opposite sides are equal.

  3. A quadrilateral is a square if and only if its opposite sides are equal.

  4. A quadrilateral is not a rectangle if and only if its opposite sides are equal.


Correct Option: B

Name the technique used in the first step of the solution to the problem below :
Verify that 5 is irrational
Solution : Let us assume that 5 is rational

  1. Counter example

  2. Direct method

  3. By Contradiction

  4. Contrapositive method


Correct Option: C

Name the technique used in the solution of the problems below :

Question: Show that the following statement is false: If n is an odd integer, then n is prime.

Solution: The given statement is in the form “if p then q” we have to show that this is false, If p then ~q.


If n= 99 is odd integer which is not a prime number. Thus, we conclude that the given statement is false.

  1. Counter example

  2. Contrapositive method

  3. Direct method

  4. By Contradiction


Correct Option: A
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