Mathematics – Class 9 – Chapter 1- Number Systems – Exercise 1.3 – NCERT Exercise Solution

1.Write the following in decimal form and say what kind of decimal expansion each has :

(i) 36/100

Solution:

Mathematics - Class 9 - Chapter 1- Number Systems - Exercise 1.3 - NCERT Exercise Solution

Hence, the decimal expansion of 36/100 is terminating.

(ii)1/11

Solution:

Mathematics - Class 9 - Chapter 1- Number Systems - Exercise 1.3 - NCERT Exercise Solution

Hence, the decimal expansion of 1/11 is non-terminating repeating.

(iii) 4 1/8

Solution:

Mathematics - Class 9 - Chapter 1- Number Systems - Exercise 1.3 - NCERT Exercise Solution

Hence, the decimal expansion of 4 1/8 is terminating.

(iv) 3/13

Solution:

Mathematics - Class 9 - Chapter 1- Number Systems - Exercise 1.3 - NCERT Exercise Solution

Here, the repeating block of digits is 230769
Hence, the decimal expansion of 3/13 is non-terminating repeating.

(v) 2/11

Solution:

Mathematics - Class 9 - Chapter 1- Number Systems - Exercise 1.3 - NCERT Exercise Solution

Here, the repeating block of digits is 18.
Hence, the decimal expansion of 2/11 is non-terminating repeating.

(vi) 329/400

Solution:

Mathematics - Class 9 - Chapter 1- Number Systems - Exercise 1.3 - NCERT Exercise Solution

Hence, the decimal expansion of 329/400 is terminating.

2.You know that 1/7 = 0.142857. Can you predict what the decimal expansions of 2/7, 3/7, 4/7, 5/7, 6/7 are, without actually doing the long division? If so, how?

[Hint: Study the remainders while finding the value of 1/7 carefully.]

Solution:

Mathematics - Class 9 - Chapter 1- Number Systems - Exercise 1.3 - NCERT Exercise Solution

3.Express the following in the form p/q where p and q are integers and q ≠ 0.

Mathematics - Class 9 - Chapter 1- Number Systems - Exercise 1.3 - NCERT Exercise Solution

Solution:

(i)

We can write given question as 0.6666….
Let, x = 0.6666…. equation(i)
Now, multiply both side by 10.
10 x = 6.6666….equation(ii)
Substracting equation (i) from equation(ii), we get
9x = 6
x = 6/9 = 2/3
Hence, required answer is 2/3

(ii)

We can write given question as 0.47777….
Let, x = 0.477777…. equation(i)
Now, multiplying both side by 10.
10 x = 4.7777….equation(ii)
Substracting equation (i) from equation(ii), we get
9x = 4.3
x = 43/90
Hence, required answer is 43/90

(iii)

We can write given question as 0.001001….
Let, x = 0.001001…. equation(i)
Now, multiply both side by 1000.
1000 x = 1.001001….equation(ii)
Substracting equation (i) from equation(ii), we get
999x = 1
x = 1/999
Hence, required answer is 1/999

4.Express 0.99999.. in the form p/q . Are you surprised by your answer? With your teacher and classmates discuss why the answer makes sense.

Solution:

Let x = 0.9999….. say equation (a)

Multiplying both sides by 10,

10x = 9.9999…. say equation (b)

Now, equation(b) – equation(a)

Mathematics - Class 9 - Chapter 1- Number Systems - Exercise 1.3 - NCERT Exercise Solution

x = 1

The difference between 1 and 0.999999 is 0.000001 which is negligible.

Hence, we can conclude that, 0.999 is too much near to 1.

Therefore, 1 as the answer can be justified.

5. 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:

According to question: In 1/17, the divisor is 17

Mathematics - Class 9 - Chapter 1- Number Systems - Exercise 1.3 - NCERT Exercise Solution
Mathematics - Class 9 - Chapter 1- Number Systems - Exercise 1.3 - NCERT Exercise Solution

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

6. Look at several examples of rational numbers in the form p/q (q ≠ 0), where p and q are integers with no common factors other than 1 and having terminating decimal representations (expansions). Can you guess what property q must satisfy?

Solution:

Let us look decimal expansion of the following terminating rational numbers:

1/2 = 0. 5, denominator q = 21

8/125 = 0.064, denominator q = 53

7/8 = 0. 875, denominator q =23

4/5 = 0. 8, denominator q = 51

Hence, we can observe that the terminating decimal may be obtained in the situation where prime factorization of the denominator of the given fractions has only powers of 2 or powers of 5 or powers of both.

7. Write three numbers whose decimal expansions are non-terminating non-recurring.

Solution:

According to question:

√2 = 1.414213562

√3 = 1.732050807568

√5 = 2.23606797

√26 =5.099019513592

√101 = 10.04987562112

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

Solution:

5/7

Mathematics - Class 9 - Chapter 1- Number Systems - Exercise 1.3 - NCERT Exercise Solution

9/11

Mathematics - Class 9 - Chapter 1- Number Systems - Exercise 1.3 - NCERT Exercise Solution

Hence, the required three different irrational numbers between 5/7 and 9/11 are:

(i)0.73073007300073000073…

(ii)0.75075007300075000075…

(iii)0.78080078008000…

9.  Classify the following numbers as rational or irrational according to their type:

(i)√23

Solution:

√23 = 4.79583152331…

Since the number is non-terminating non-recurring, not perfect square.Hence, it is an irrational number.

(ii)√225

Solution:

√225 = 15 = 15/1

Since the number can be represented in p/q form, and it perfect square. Hence, it is a rational number.

(iii) 0.3796

Solution:

Since the number,0.3796, is terminating, and perfect square. Hence it is a rational number.

(iv) 7.478478

Solution:

The number,7.478478, is non-terminating but recurring. Hence, it is a rational number.

(v) 1.101001000100001…

Solution:

Since the number,1.101001000100001…, is non-terminating non-repeating (non-recurring). Hence,  it is an irrational number.

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