NCERT Solutions for Class 10 Maths Chapter 1 Ex 1.4: Exercise 1.4 of Chapter 1 Real Numbers focuses on the application of the Fundamental Theorem of Arithmetic which states that every composite number can be uniquely expressed as a product of prime numbers.
By solving these questions students develop a deeper understanding of how numbers can be decomposed into their prime factors which is important for further topics like HCF, LCM, and number theory. The NCERT Solutions for Exercise 1.4 provide step-by-step solutions, helping students learn the process of prime factorization and enhancing their problem-solving skills.NCERT Solutions for Class 10 Maths Chapter 1 Ex 1.4 PDF
1. Without actually performing the long division, state whether the following rational numbers will have a terminating decimal expansion or a non-terminating repeating decimal expansion.
(i) 13/3125 (ii) 17/8 (iii) 64/455 (iv) 15/1600 (v) 29/343 (vi) 23/(2 3 5 2 ) (vii) 129/(2 2 5 7 7 5 ) (viii) 6/15 (ix) 35/50 (x) 77/210
Solutions:
Note: If the denominator has only factors of 2 and 5 or in the form of 2 m ×5 n, then it has a terminating decimal expansion.
If the denominator has factors other than 2 and 5, then it has a non-terminating decimal expansion.(i) 13/3125
Factorising the denominator, we get 3125 = 5 × 5 × 5 = 5 5 Since the denominator has only 5 as its factor, 13/3125 has a terminating decimal expansion.(ii) 17/8
Factorising the denominator, we get8 = 2×2×2 = 2 3
Since the denominator has only 2 as its factor, 17/8 has a terminating decimal expansion.(iii) 64/455
Factorising the denominator, we get 455 = 5×7×13 Since the denominator is not in the form of 2 m × 5 n , 64/455 has a non-terminating decimal expansion.(iv) 15/ 1600
Factorising the denominator, we get 1600 = 2 6 ×5 2 Since the denominator is in the form of 2 m × 5 n , 15/1600 has a terminating decimal expansion.(v) 29/343
Factorising the denominator, we get 343 = 7×7×7 = 7 3 Since the denominator is not in the form of 2 m × 5 n , 29/343 has a non-terminating decimal expansion.(vi)23/(2 3 5 2 )
Clearly, the denominator is in the form of 2 m × 5 n . Hence, 23/ (2 3 5 2 ) has a terminating decimal expansion.(vii) 129/(2 2 5 7 7 5 )
As you can see, the denominator is not in the form of 2 m × 5 n . Hence, 129/ (2 2 5 7 7 5 ) has a non-terminating decimal expansion.(viii) 6/15
6/15 = 2/5 Since the denominator has only 5 as its factor, 6/15 has a terminating decimal expansion.(ix) 35/50
35/50 = 7/10 Factorising the denominator, we get 10 = 2 × 5 Since the denominator is in the form of 2 m × 5 n , 35/50 has a terminating decimal expansion.(x) 77/210
77/210 = (7× 11)/ (30 × 7) = 11/30 Factorising the denominator, we get 30 = 2 × 3 × 5 As you can see, the denominator is not in the form of 2 m × 5 n . Hence, 77/210 has a non-terminating decimal expansion.2. Write down the decimal expansions of those rational numbers in Question 1 above which have terminating decimal expansions.
Solutions:
(i) 13/3125
(ii) 17/8
(iii) 64/455 has a non-terminating decimal expansion.
(iv)15/ 1600
(v) 29/ 343 has a non-terminating decimal expansion.
(vi)23/ (2 3 5 2 ) = 23/(8×25)= 23/200
(vii) 129/ (2 2 5 7 7 5 ) has a non-terminating decimal expansion.
(viii) 6/15 = 2/5
(ix) 35/50 = 7/10
(x) 77/210 has a non-terminating decimal expansion.
3. The following real numbers have decimal expansions, as given below. In each case, decide whether they are rational or not. If they are rational and of the form, p q, what can you say about the prime factors of q?
(i) 43.123456789
(ii) 0.120120012000120000. . .
Solutions:
(i) 43.123456789 Since it has a terminating decimal expansion, it is a rational number in the form of p/q, and q has factors of 2 and 5 only. (ii) 0.120120012000120000. . . Since it has a non-terminating and non-repeating decimal expansion, it is an irrational number.