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NCERT
SOLUTIONS
CLASS - 8TH
aglase .co
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Book : Mathematics Ncert Solutions | Chapter-1 Maths
Class : 8th
Subject : Maths
Chapter : 1
Chapter Name : Rational Numbers
Exercise 1.1
Q1 Using appropriate properties nd.
2 3 5 3 1 2 3 1 3 1 2
(i) − × + − × (ii) × (− ) − × + ×
3 5 2 5 6 5 7 6 2 14 5
Answer. (i)
2 3 5 3 1 2 3 3 1 5
− × + − × = − × − × +
3 5 2 5 6 3 5 5 6 2
(Using commutativity of rational numbers)
3 2 1 5
= (− ) × ( + ) + (Distributivity)
5 3 6 2
3 2×2+1 5 3 5 5
= (− ) × ( ) + = (− ) × ( ) +
5 6 2 5 6 2
3 5 −3+5×3 −3+15
= (− ) + = ( ) = ( )
6 2 6 6
12
= = 2
6
(ii) (By commutativity)
2 3 1 3 1 2 2 3 1 2 1 3
× (− ) − × + × = × (− ) + × − ×
5 7 6 2 14 5 5 7 14 5 6 2
(By distributivity)
2 3 1 1
= × (− + ) −
5 7 14 4
2 −3×2+1 1
= × ( ) −
5 14 4
2 −5 1
= × ( ) −
5 14 4
1 1
= − −
7 4
−4−7 −11
= =
28 28
Q2 Write the additive inverse of each of the following.
2 −5 −6 2 19
(i) (ii) (iii) (iv) (v)
8 9 −5 −9 −6
Answer (i)Additive inverse = − 2
8
(ii)Additive inverse =
5
9
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Book : Mathematics Ncert Solutions | Chapter-1 Maths
(iii)
−6 6
=
−5 5
Additive inverse = −
6
−5
(iv) 2 −2
=
−9 9
Additive inverse = 2
9
(v)
19 −19
=
−6 6
Additive inverse = 19
6
Q3 Verify that – (– x) = x for.
.
11 13
(i) x = (ii) x = −
15 17
Answer.
11
(i) x =
15
11
x=
The additive inverse of 15 11 11 11
− x = − as + (− ) = 0
is 15 15 15
This equality
11 11
+ (− ) = 0
15 15
11
−
represents that the additive inverse of 15
is 15 or it
11 11
can be said that − (− ) =
15 15 i.e., −(−x)=x
13
(ii)
x = −
17
The additive inverse of x = − 13
17
is − x =
13
17
as −
13
17
+
13
17
= 0
13 13 13 13
This equality − + = 0 represents that the additive inverse of is i.e.,
17 17 17 −17
−(−x) = x
Q4 Find the multiplicative inverse of the following.
−13 1 −5 −3 −2
(i) − 13 (ii) (iii) (iv) × (v) − 1 × ( vi) − 1
19 5 8 7 5
Answer. (i) 13
Multiplicative inverse =
1
−13
(ii) 13
−19
Multiplicative inverse =− 19
13
(iii)
1
5
Multiplicative inverse = 5
(iv)− × − = 5
8
3
7
15
56
Multiplicative inverse = 56
15
(v)−1 × − 2
5
=
2
5
Multiplicative inverse =
5
2
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Book : Mathematics Ncert Solutions | Chapter-1 Maths
(vi) -1
Multiplicative inverse = -1
Q5 Name the property under multiplication used in each of the following.
(i)
−4 −4 4 13 −2 −2 −13
× 1 = 1 × = − (ii) − × = ×
5 5 5 17 7 7 17
(iii)
−19 29
× = 1
29 −19
Answer. (i) 1 is the multiplicative identity.
(ii) Commutativity
(iii) Multiplicative inverse
Q6 Multiply by the reciprocal of .
6 −7
13 16
Answer. 6
13
× ( Reciprocal of −
7
16
) =
6
13
× −
16
7
= −
96
91
Q7 Tell what property allows you to compute 1
3
× (6 ×
4
3
) as (
1
3
× 6) ×
4
3
Answer. Associativity
Q8 Is 8
9
the multiplicative inverse of −1 1
8
? Why or why not?
Answer. If it is the multiplicative inverse, then the product should be 1.
However, here, the product is not 1 as
8 1 8 9
× (−1 ) = × (− ) = −1 ≠ 1
9 8 9 8
Q9 Is 0.3 the multiplicative inverse of 3 1
3
? Why or why not?
Answer. 3 1
3
=
10
3
1
0.3 ×
3
3 = 0.3 ×
10
3
=
3
10
×
10
3
= 1 Here, the product is 1. Hence, 0.3 is the multiplicative
inverse of 3 1
3
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Book : Mathematics Ncert Solutions | Chapter-1 Maths
Q10 Write.
(i) The rational number that does not have a reciprocal.
(ii) The rational numbers that are equal to their reciprocals.
(iii) The rational number that is equal to its negative.
Answer. (i) 0 is a rational number but its reciprocal is not de ned.
(ii) 1 and —1 are the rational numbers that are equal to their reciprocals.
(iii) 0 is the rational number that is equal to its negative.
Page : 15 , Block Name : Exercise 1.1
Q11 Fill in the blanks.
(i) Zero has ________ reciprocal.
(ii) The numbers ________ and ________ are their own reciprocals
(iii) The reciprocal of – 5 is ________.
(iv) Reciprocal of 1 x , where x ≠ 0 is ________.
(v) The product of two rational numbers is always a _______.
(vi) The reciprocal of a positive rational number is ________.
Answer. (i) No
(ii) 1 , -1
(iii) − 1
5
(iv) x
(v) Rational number
(vi) Positive rational number
Page : 15 , Block Name : Exercise 1.1
Exercise 1.2
Q1 Represent these numbers on the number line. (i) 7
4
(ii) 5
6
Answer. (i) can be represented on the number line as follows.
7
4
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Book : Mathematics Ncert Solutions | Chapter-1 Maths
Page : 20 , Block Name : Exercise 1.2
Q2 Represent on the number line.
−2 −5 −9
, ,
11 11 11
Answer.
Page : 20 , Block Name : Exercise 1.2
Q3 Write ve rational numbers which are smaller than 2.
Answer. 2 can be represented as 14
7
Therefore, ve rational numbers smaller than 2 are
13 12 11 10 9
, , , ,
7 7 7 7 7
Page : 20 , Block Name : Exercise 1.2
Q4 Find ten rational numbers between and
−2 1
5 2
Answer. and can be represented as − and respectively.
−2 1 8 10
5 2 20 20
Therefore, ten rational numbers between and are
−2 1
5 2
7 6 5 4 3 2 1 1 2
− ,− ,− ,− ,− ,− ,− , 0, ,
20 20 20 20 20 20 20 20 20
Page : 20 , Block Name : Exercise 1.2
Q5 Find ve rational numbers between.
(i) and
2
3
4
5
(ii)
−3 5
and
2 3
(iii) 1
4
and
1
2
Answer. (i) 2
3
and
4
5
can be represented as 30
45
and
36
45
respectively.
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Book : Mathematics Ncert Solutions | Chapter-1 Maths
Therefore, ve rational numbers between are
2 4 31 32 33 34 35
and , , , ,
3 5 45 45 45 45 45
(ii) can be represented as − respectively
−3 5 9 10
and and
2 3 6 6
Therefore, ve rational numbers between are −
−3 5 8 7 5 4
and ,− , −1, − ,−
2 3 6 6 6 6
(iii) 1
4
and
1
2
can be represented as 8
32
and
16
32
Therefore, ve rational numbers between 1
4
and
1
2
are 9
32
,
10
32
,
11
32
,
12
32
,
13
32
Page : 20 , Block Name : Exercise 1.2
Q6 Write ve rational numbers greater than -2.
Answer. -2 can be represented as − 14
7
.
Therefore, ve rational numbers greater than —2 are
13 12 11 10 9
− ,− ,− ,− ,−
7 7 7 7 7
Page : 20 , Block Name : Exercise 1.2
Q7 Find ten rational numbers 3
5
and
3
4
.
Answer. can be represented as respectively.
3 3 48 60
and and
5 4 80 80
Therefore, ten rational numbers between 3
5
and
3
4
are
49 50 51 52 53 54 55 56 57 58
, , , , , , , , ,
80 80 80 80 80 80 80 80 80 80
Page : 20 , Block Name : Exercise 1.2
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