Math Class IX 1 Question Bank RATIONAL AND IRRATIONAL NUMBERS Q.1. Without actual division find which of the following rationals are terminating decimal: (i) 9 25 (ii) 7 12 (iii) 121 125 (iv) 37 78 Ans. (i) In 9 25 , the prime factors of denominator 25 are 5, 5. Thus it is terminating decimal. (ii) In 7 12 , the prime factors of denominator 12 are 2, 2 and 3. Thus it is not terminating decimal. (iii) In 121 125 , the prime factors of denominator 125 are 5, 5 and 5. Thus it is terminating decimal. (iv) In 37 78 , the prime factors of denominator 78 are 2, 3 and 13. Thus it is not terminating decimal. Q.2. Represent each of the following as a decimal number. (i) 4 15 (ii) 5 2 12 (iii) 31 5 55 Ans. (i) In 4 15 , using long division method: 0.266... 15 4.0000 30 100 90 100 90 10 Hence, 4 0.266... 0.26. 15 = =
22
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Math Class IX 1 Question Bank
RATIONAL AND
IRRATIONAL NUMBERS Q.1. Without actual division find which of the following rationals are
terminating decimal:
(i) 9
25 (ii)
7
12 (iii)
121
125 (iv)
37
78
Ans. (i) In 9
25, the prime factors of denominator 25 are 5, 5. Thus it is terminating decimal.
(ii) In 7
12, the prime factors of denominator 12 are 2, 2 and 3. Thus it is not
terminating decimal.
(iii) In 121
125, the prime factors of denominator 125 are 5, 5 and 5. Thus it is
terminating decimal.
(iv) In 37
78, the prime factors of denominator 78 are 2, 3 and 13. Thus it is not
terminating decimal.
Q.2. Represent each of the following as a decimal number.
(i) 4
15 (ii)
52
12 (iii)
315
55
Ans. (i) In 4
15, using long division method:
0.266...
15 4.0000
30 100
90
100
90
10
Hence, 4
0.266... 0.26.15
= =
Math Class IX 2 Question Bank
(iv) In 31
555
, using long division method:
0.5636363
55 31.0000000
275 350
330
200
165
350
330
200
165
350
330
200
165
35
Hence, 31
5 5.5636363... 5.563.55
= =
(iii) In 5
212
, using long division method:
0.4166...
12 5.000
48 20
12
80
72
80
72
8
Hence, 5
2 2.4166... 2.416.12
= =
Q.3. Express each of the following as a rational number in the form of p
q,
where q ≠ 0 .
(i) 0.6 (ii) 0.43 (iii) 0.227 (iv) 0.2104
Ans. (i) Let 0.6 0.6666x = = ...(i)
Multiplying both sides of eqn. (i) by 10, we get
10 6.6666x = ...(ii)
Subtracting eqn. (i) from eqn. (ii), we get
10 6.6666
0.6666
x
x
=
=
9 6x = 6 2
9 3x⇒ = = Hence, required fraction
2.
3=
(ii) Let 0.43 0.43434343x = = ...(i)
Multiplying both sides of eqn. (i) by 100, we get
100 43.434343x = ...(ii)
Subtracting eqn. (i) from eqn. (ii), we get
Math Class IX 3 Question Bank
100 43.434343
0.434343
x
x
=
=
99 43x = ⇒ 43
99 4399
x x= ⇒ =
Hence, required fraction 43
.99
p
q=
(iii) Let 0.227 0.2272727...x = = ...(i)
Multiplying both sides of eqn. (i) by 10, we get
10 2.272727...x = ...(ii)
Multiplying both sides of eqn. (ii) by 100, we get
1000 227.272727...x = ...(iii)
Subtracting eqn. (ii) from (iii), we get
1000 227.272727...
10 2.272727...
x
x
=
=
990 225x = ⇒ 225 5
990 225990 22
x x= ⇒ = =
Hence, required fraction 5
.22
p
q=
(iv) Let 0.2104 0.2104104104...x = = ...(i)
Multiplying both sides of eqn. (i) by 10, we get
10 2.104104104...x = ...(ii)
Multiplying both sides of eqn. (ii) by 1000, we get
10000 2104.104104104...x = ...(iii)
Subtracting eqn. (ii) from (iii), we get
10000 2104.104104104
10 2.104104104
x
x
=
=
9990 2102x = ⇒ 2102 1051
9990 21029990 4995
x x= ⇒ = =
Hence, required fraction 1051
.4995
=
Math Class IX 4 Question Bank
Q.4. Express each of the following as a vulgar fraction.
(i) 3.146 (ii) 4.324
Ans. Let 3.146 3.146146x = = ...(i)
Multiplying both sides of eqn. (i) by 1000, we get
1000 3146.146146146x = ...(ii)
Subtracting eqn. (i) from eqn. (ii), we get
1000 3146.146146146
3.146146146
x
x
=
=
999 3143x = ⇒ 3143
999 3143999
x x= ⇒ =
Hence, required vulgar fraction3143
999= .
(ii) Let 4.324 4.324242424x = = ...(i)
Multiplying both sides of eqn. (i) by 10, we get
10 43.24242424x = ...(ii)
Multiplying both sides of eqn. (ii) by 100, we get
1000 4324.24242424x = ...(iii)
Subtracting eqn. (ii) from eqn. (iii), we get
1000 4324.24242424
10 43.24242424
x
x
=
=
990 4281x = ⇒ 4281 1427
990 4281990 330
x x= ⇒ = =
Hence, required vulgar fraction 1427
330= .
Q.5. Insert one rational number between:
(i) 3 7
and5 9
(ii) 8 and 8.04
Ans. If a and b are two rational numbers, then between these two numbers, one
rational number will be ( )
.2
a b+
Required rational number between 3
5 and
7
9
1 3 7 1 27 35
2 5 9 2 45
+ = + =
1 62 31
2 45 45= × = ∴
3 31 7.
5 45 9< <
Math Class IX 5 Question Bank
(ii) Required rational number between 8 and 8.04
1 1
(8 8.04) (16.04) 8.022 2
= + = = ∴ 8 8.02 8.04< <
Q.6. Insert two rational numbers between 3 1
and 14 5
Ans. 3 1 3 6
and 1 and4 5 4 5
⇒ ⇒ 3 1 3 6 6
4 2 4 5 5
< + <
3 1 15 24 6
5 2 20 5
+ ⇒ < <
3 1 39 6
4 2 20 5
⇒ < <
3 39 6
4 40 5⇒ < <
3 39 1 39 6 6
4 40 2 40 5 5
⇒ < < + <
3 39 1 39 48 6
4 40 2 40 5
+ ⇒ < < <
3 39 1 87 6
4 40 2 40 5
⇒ < < <
3 39 87 6
4 40 80 5⇒ < < <
Hence, required rational numbers are 39
40 and
87.
80
Q.7. Insert three rational numbers between
(i) 4 and 5 (ii) 1
2 and
3
5
(iii) 4 and 4.5 (iv) 1
23
and 2
33
(v) −1
2 and
1
3
Ans. (i) The given numbers are 4 and 5.
As, 4 5<
1 4 5 9
4 5 4 52 1 2
+ ⇒ < < ⇒ < <
4 4.5 5⇒ < < ...(i)
Again, 1 9 9
4 42 2 2
< + <
4 4.25 4.5⇒ < < ...(ii)
Again, 1
4.5 5 4.5 (4.5 5) 5 4.5 4.75 52
< ⇒ < + < ⇒ < < ...(iii)
∴ From eqn. (i), (ii) and (iii), we get 4 4.25 4.5 4.75 5.< < < <
Thus, required rational numbers between 4 and 5 are 4.25, 4.75 and 4.5.
Math Class IX 6 Question Bank
(ii) The given numbers are 1
2 and
3
5
As, 1 3
2 5<
1 1 1 3 3
2 2 2 5 5
⇒ < + <
1 1 5 6 3
2 2 10 5
+ ⇒ < <
1 1 11 3
2 2 10 5
⇒ < <
1 11 3
2 20 5⇒ < <
Again, 1 1 1 11 3
2 2 2 20 5
< + <
⇒
1 1 21 3
2 2 20 5
< <
1 21 3
2 40 5< < ...(ii)
Again, 11 3
20 5< ⇒
11 1 11 3 3
20 2 20 5 5
< + <
1 1 23 3
2 2 20 5
⇒ < <
1 23 3
2 40 5⇒ < < ...(iii)
From eqn. (i), (ii) and (iii), we get
1 21 11 23 3
2 40 20 40 15< < < <
Thus, required rational numbers between 1
2 and
3
5 are
21 11,
40 20 and
23.
40
(iii) The given numbers are 4 and 4.5
As 4 4.5<1
4 (4 4.5) 4.52
⇒ < + <
4 4.25 4.5⇒ < < ...(i)
14 (4 4.25) 4.25
2⇒ < + < 4 4.125 4.25⇒ < < ...(ii)
Again, 4.25 4.5<
14.25 (4.25 4.5) 4.5
2⇒ < + + 4.25 4.375 4.5⇒ < < ...(iii)
From eqn. (i), (ii) and (iii), we have 4 4.125 4.25 4.375 4.5< < < <
Thus, required rational numbers between 4 and 4.5 are 4.125, 4.25 and 4.375.
Math Class IX 7 Question Bank
(iv) The given numbers are 1 2 7 11
2 and 3 i.e., and .3 3 3 3
As 7 11
3 3<
7 1 7 11 11
3 2 3 3 3
⇒ < + <
7 1 18 11
3 2 3 3
⇒ < <
7 18 11
3 6 3⇒ < <
7 113
3 3⇒ < < ...(i)
Again, 7 1 7 3
33 2 3 1
< + <
7 8
33 3
< < ...(ii)
Again, 11
33
<
1 11 11
3 32 3 3
< + <
⇒
1 20 113
2 3 3
< <
10 11
33 3
< < ...(iii)
From eqn. (i), (ii) and (iii), we get
7 8 10 11
3 .3 3 3 3
< < < <
Thus required rational numbers between 1 2
2 and 3 i.e.,3 3
7
3 and
11
3 are
8, 3
3 and
10.
3
Q.8. Find the decimal representation of 1
7 and
2
7. Deduce from the decimal
representation of 1
,7
without actual calculation, the decimal representa-
tion of 3 4 5
, ,7 7 7
and 6
.7
Math Class IX 8 Question Bank
Ans. Decimal representation of 1
7 using long division method.
0.142871
7 1.000000
7 30
28
20
14
60
56
40
35
50
49
10
7
3
Q.9. State, whether the following numbers are rational or irrational:
(i) ( )2
2 + 2 (ii) ( )( )−5 + 5 5 5
Ans. (i) ( )2
2 2 4 2 2 2 2 6 4 2+ = + + × × = +
Hence, it is an irrational number.
(iii) ( ) ( ) ( ) ( )22
5 5 5 5 5 5+ − = − [Using 2 2( )( )a b a b a b+ − = − ]