# Important Questions Class 9 Maths Chapter 1 Number System

Important questions for Class 9 Maths Chapter 1 Number system are given here. These practice questions will help the students to build a better understanding of the Number system concept in Maths. These Class 9 Chapter 1 questions are important for CBSE Class 9 Maths exams. These important questions give an overview of the question types that are asked in the final exams and so students are able to face the exams more confidently.

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## Number System Important Questions For Class 9 (Chapter 1)

Below given important Number system questions for 9th class students will help them to get acquainted with a wide variation of questions and thus, develop problem-solving skills.

Q.1: Find five rational numbers between 1 and 2.

Solution:

We have to find five rational numbers between 1 and 2.

So, let us write the numbers with denominator 5 + 1 = 6

Thus, 6/6 = 1, 12/6 = 2

From this, we can write the five rational numbers between 6/6 and 12/6 as:

7/6, 8/6, 9/6, 10/6, 11/6

Q.2: Find five rational numbers between 3/5 and 4/5.

Solution:

We have to find five rational numbers between 3/5 and 4/5.

So, let us write the given numbers by multiplying with 6/6, (here 6 = 5 + 1)

Now,

3/5 = (3/5) × (6/6) = 18/30

4/5 = (4/5) × (6/6) = 24/30

Thus, the required five rational numbers will be: 19/30, 20/30, 21/30, 22/30, 23/30

Q.3: Locate 3 on the number line.

Solution:

Construct BD of unit length perpendicular to OB (here, OA = AB = 1 unit) as shown in the figure.

By Pythagoras theorem,

OD = √(2 + 1) = √3

Taking O as the centre and OD as radius, draw an arc which intersects the number line at the point Q using a compass.

Therefore, Q corresponds to the value of √3 on the number line.

Q.4: Are the square roots of all positive integers irrational? If not, give an example of the square root of a number that is a rational number.

Solution:

No, since the square root of a positive integer 16 is equal to 4. Here, 4 is a rational number.

Q.5: Find the decimal expansions of 10/3, 7/8 and 1/7.

Solution:

Therefore, 10/3 = 3.3333…

7/8 = 0.875

1/7 = 0.1428571…

Q.6: Show that $0.3333… = 0.\bar{3}$ can be expressed in the form p/q, where p and q are integers and q ≠ 0.

Solution:

Let x = 0.3333….

Multiply with 10,

10x = 3.3333…

Now, 3.3333… = 3 + x (as we assumed x = 0.3333…)

Thus, 10x = 3 + x

10x – x = 3

9x = 3

x = 1/3

Therefore, 0.3333… = 1/3. Here, 1/3 is in the form of p/q and q ≠ 0.

Q.7: What can the maximum number of digits be in the repeating block of digits in the decimal expansion of 1/17? Perform the division to check your answer.

Solution:

Thus, 1/17 = 0.0588235294117647….

Therefore, 1/17 has 16 digits in the repeating block of digits in the decimal expansion.

Q.8: Find three different irrational numbers between the rational numbers 5/7 and 9/11.

Solution:

The given two rational numbers are 5/7 and 9/11.

5/7 = 0.714285714…..

9/11 = 0.81818181……

Hence, the three irrational numbers between 5/7 and 9/11 can be:

0.720720072000…

0.730730073000…

0.808008000…

Q.9: Visualise 3.765 on the number line, using successive magnification.

Solution:

Visualisation of 3.765 on the number line, using successive magnification is given below:

Q.10: Add 22+ 53 and 2 – 33.

Solution:

(2√2 + 5√3) + (√2 – 3√3)

= 2√2 + 5√3 + √2 – 3√3

= (2 + 1)√2 + (5 – 3)√3

= 3√2 + 2√3

Q.11: Simplify: (√3+√7) (√3-√7).

Solution:

(√3 + √7)(√3 – √7)

Using the identity (a + b)(a – b) = a2 – b2,

(√3 + √7)(√3 – √7) = (√3)2 – (√7)2

= 3 – 7

= -4

Q.12: Rationalise the denominator of 1/[7+3√3].

Solution:

1/(7 + 3√3)

By rationalizing the denominator,

= [1/(7 + 3√3)] [(7 – 3√3)/(7 – 3√3)]

= (7 – 3√3)/[(7)2 – (3√3)2]

= (7 – 3√3)/(49 – 27)

= (7 – 3√3)/22

Q.13: Represent √(9.3) on the number line.

Solution:

Representation of √9.3 on the number line is given below:

Q.14: Simplify:

(i) 72/3.71/5
(ii) 101/2/101/4

Solution:

(i) 72/3.71/5

Bases are equal, so add the powers.

7(2/3 + 1/5)

= 7(10 + 3)/15

= 713/15

(ii) 101/2/101/4

Bases are equal, so subtract the powers.

= 10 (1/2 – 1/4)

= 101/4

Q.15:  What is the product of a rational and an irrational number?
a) Always an integer
b) Always a rational number
c) Always an irrational number
d) Sometimes rational and sometimes irrational

Correct answer: Option (c)

Explanation:

The product of a rational and an irrational number is always an irrational number.

For example, 2 is a rational number and √3 is irrational. Thus, 2√3 is always an irrational number.

Q.16: What is the value of (256)0.16 X (256)0.09?
a) 4
b) 16
c) 64
d) 256.25

Correct answer: Option (a)

(256)0.16 x (256)0.09 = (256)(0.16 + 0.09)

= (256)0.25

= (256)(25/100)

= (256)(1/4)

= (44)(1/4)

= 44(1/4)

= 4

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