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Exponents And Powers

Class 7th Mathematics CBSE Solution

Exercise 13.1
Question 1.

Find the value of:

(i) 26

(ii) 93

(iii) 112

(iv) 54


Answer:

(i) In the given question,

We have to find the value of 26


26 = 2 × 2 × 2 × 2 × 2 × 2


= 64


(ii) In the given question,


We have to find the value of 93


93 = 9 × 9 × 9


= 729


(iii) In the given question,


We have to find the value of 112


112 = 11 × 11


= 121


(iv) In the given question,


We have to find the value of 54


54 = 5 × 5 × 5 × 5


= 625



Question 2.

Express the following in exponential form:

(i) 6 × 6 × 6 × 6

(ii) t × t

(iii) b × b × b × b

(iv) 5 × 5 × 7 × 7 × 7

(v) 2 × 2 × a × a

(vi) a × a × c × c × c × c × d


Answer:

(i) We have,

6 × 6 × 6 × 6


= 61+1+1+1


= 64


(ii) We have,


t × t


= t1+1


= t2


(iii) We have,


b × b × b × b


= b1+1+1+1


= b4


(iv) We have,


5 × 5 × 7 × 7 × 7


= 51+1 × 71+1+1


= 52 × 73


(v) We have,


2 × 2 × a × a


= 21+1 × a1+1


= 22 × a2


(vi) We have,


a × a × a × c × c × c × c × d


= a1+1+1 × c1+1+1+1 × d1


= a3 × c4 × d


Question 3.

Express each of the following numbers using exponential notation:

(i) 512

(ii) 343

(iii) 729

(iv) 3125


Answer:

(i) 512

We have,


512 = 2 × 2 × 2 × 2 × 2 × 2 × 2 × 2 × 2


= 29


(ii) 343

We have,


343 = 7 × 7 × 7


= 73


(iii) 729

We have,


729 = 3 × 3 × 3 × 3 × 3 × 3


= 36


(iv) 3125




We have,


3125 = 5 × 5 × 5 × 5 × 5


= 55


Question 4.

Identify the greater number, wherever possible, in each of the following.

(i) 43 or 34

(ii) 53 or 35

(iii) 28 or 82

(iv) 1002 or 2100

(v) 210 or 102


Answer:

(i) We have, 43 or 34

On simplifying we get,


43 = 4 × 4 × 4


= 64


And,


34 = 3 × 3 × 3 × 3


= 81


Clearly,


81 > 64


Thus,


34 > 43


(ii) We have, 53 or 35


On simplifying we get,


53 = 5 × 5 × 5


= 125


35 = 3 × 3 × 3 × 3 × 3


= 243


Clearly,


243 > 125


Thus,


35 > 53


(iii) We have, 28 or 82


On simplifying we get,


28 = 2 × 2 × 2 × 2 × 2 × 2 × 2 × 2


= 256


82 = 8 × 8


= 64


Clearly,


256 > 64


Thus,


28 > 82


(iv) We have, 1002 or 2100


On simplifying we get,


1002 = 100 × 100


= 10000


210 = 2 × 2 × 2 × 2 × 2 × 2 × 2 × 2 × 2 × 2


= 1024


Now,


2100 = 1024 × 1024 × 1024 × 1024 × 1024 × 1024 × 1024 × 1024 × 1024 × 1024


Clearly,


2100 > 10000


Thus,


2100 > 1002


(v) W have, 210 or 102


On simplifying we get,


102 = 10 × 10


= 100


210 = 2 × 2 × 2 × 2 × 2 × 2 × 2 × 2 × 2 × 2


= 1024


Clearly,


1024 > 100


Thus,


210 > 102



Question 5.

Express each of the following as product of powers of their prime factors:

(i) 648

(ii) 405

(iii) 540

(iv) 3600


Answer:

(i) On simplifying we get,

648 = 2 × 2 × 2 × 3 × 3 × 3 × 3


= 23 × 34


(ii) On simplifying we get,


405 = 3 × 3 × 3 × 3 × 5


= 34 × 5


(iii) On simplifying we get,


540 = 2 × 2 × 3 × 3 × 3 × 5


= 22 × 33 × 5



(iv) On simplifying we get,


3600 = 2 × 2 × 2 × 2 × 3 × 3 × 5 × 5


= 24 × 32 × 52


Question 6.

Simplify:
(i) 2 × 103
(ii) 72 × 22
(iii) 23 × 5
(iv) 3 × 44
(v) 0 × 102
(vi) 52 × 33
(vii) 24 × 32
(viii) 32 × 104


Answer:

(i) We have,

2 × 103 = 2 × 10 × 10 × 10

= 2 × 1000

= 2000

(ii) We have,

72 × 22 = 7 × 7 × 2 × 2

= 49 × 4

= 196

(iii) We have,

23 × 5 = 2 × 2 × 2 × 5

= 8 × 5

= 40

(iv) We have,

3 × 44 = 3 × 4 × 4 × 4 × 4

= 3 × 256

= 768

(v) We have,

0 × 102 = 0 × 10 × 10

= 0 × 100

= 0

(vi) We have,

52 × 33 = 5 × 5 × 3 × 3 × 3

= 25 × 27

= 675

(vii) We have,

24 × 32 = 2 × 2 × 2 × 2 × 3 × 3

= 16 × 9

= 144

(viii) We have,

32 × 104 = 3 × 3 × 10 × 10 × 10 × 10

= 9 × 10000

= 90000


Question 7.

Simplify:

(i) (-4)3

(ii) (-3) × (-2)3

(iii) (-3)2 × (-5)2

(iv) (-2)3 × (-10)3


Answer:


(i)
We simplify the given expression (-4)3 as:

(-4)3 = (-4) × (-4) × (-4)

= - 64


(ii) We simplify the given expression (-3) × (-2)3 as:


(-3) × (-2)3 = (-3) × (-2) × (-2) × (-2)


= (-3) × (-8)


= 24


(iii) We simplify the given expression (-3)2 × (-5)2 as:


(-3)2 × (-5)2 = (-3) × (-3) × (-5) × (-5)


= 9 × 25


= 225


(iv) We simplify the given expression (-2)3 × (-10)3 as:


(-2)3 × (-10)3 = (-2) × (-2) × (-2) × (-10) × (-10) × (-10)


= (-8) × (-1000)


= 8000


Question 8.

Compare the following numbers:
(i) 2.7 × 1012; 1.5 × 108
(ii) 4 × 1014; 3 × 1017


Answer:

(i) We have,

2.7 × 1012 and 1.5 × 108

Since,


2.7 is greater than 1.5 and 1012 is also greater than 108


Hence,


2.7 × 1012 > 1.5 × 108


(ii) We have,


4 × 1014 and 3 × 1017


Since,


4 is greater than 3 but 1017 is greater than 1014


Hence,


3 × 1017 > 4 × 1014



Exercise 13.2
Question 1.

Using laws of exponents simplify and write the answer in exponential form:

(i) 32 × 34 × 38

(ii) 615 610

(iii) a3 × a2

(iv) 7x × 72

(v) (52)3 53

(vi) 25 × 55

(vii) a4 × b4

(viii) (34)3

(ix) (220 215) × 23

(x) (8t 82)


Answer:

(i) We know that, (am × an = am + n)

Thus,


32 × 34 × 38


= (3)2 + 4 + 8


= 314


(ii) We have,


615 610


We know that,


(am an = am - n)


Thus,


615 610


= (6)15 - 10


= 65


(iii) We have,


a3 × a2


We know that,


(am × an = am + n)


Therefore,


a3 × a2


= (a)3 + 2


= a5


(iv) We have,


7x × 72


We know that,


(am × an = am + n)


Thus,


7x × 72


= (7)x + 2


(v) We have,


(52)3 53


Using identity:


(am)n = am × n


= 52 × 3 53


= 56 53


We know that,


(am an = am - n)


Thus,


56 53


= (5)6 - 3


= 53


(vi) We have,


25 × 55


We know that,


[am × bm = (a × b)m]


Thus,


25 × 55


= (2 × 5)5 + 5


= 105


(vii) We have,


a4 × b4


We know that,


[am × bm = (a × b)m]


Thus,


a4 × b4


= (a × b)4


(viii) We have,


(34)3


We know that,


(am)n = amn)


Thus,


(34)3


= (34)3


= 312


(ix) We have,


(220 215) × 23


We know that,


(am an = am - n)


Thus,


(220 - 15) × 23


= (2)5 × 23


We know that,


(am × an = am + n)


Thus,


(2)5 × 23


= (25 + 3)


= 28


(x) We have,


(8t 82)


We know that,


(am an = am - n)


Thus,


(8t 82)


= (8t – 2)


Question 2.

Simplify and express each of the following in exponential form:

(i)

(ii)

(iii)

(iv)

(v)

(vi)

(vii)

(viii)

(ix)

(x)

(xi)

(xii)


Answer:

(i) In the above question,

We have to simplify the given numbers into exponential form:


∴ We have,


=


=


=


= (am × an = am + n)


Using identity: (am an = am - n)


= 25 - 5 × 34 – 1


= 2033


= 1 × 33


= 33


(ii) In the above question,


We have to simplify the given numbers into exponential form:


[(52)3 × 54] 57


Using identity: (am)n = amn)


= [(5)2 × 3 × 54] 57


= [(5)6 × 4] 57


Using identity: (am × an = am + n)


= [56 + 4] 57


Using identity: (am an = am - n)


Therefore,


= 510 57


= 510 – 7


= 53


(iii) In the above question,


We have to simplify the given numbers into exponential form:


We have,


254 53


= (5 × 5)4 53


Using identity: (am)n = amn


= 52 × 4 53


= 58 53


Using identity: (am an = am - n)


58 53


= 58 – 3


= 55


(iv) In the above question,


We have to simplify the given numbers into exponential form:


We have,



=


Using identity: (am an = am - n)


= 31 - 1 × 72 – 1 × 118 – 3


= 30 × 71 × 115


= 1 × 7 × 115


= 7 × 115


(v) In the above question,


We have to simplify the given numbers into exponential form:


We have,



Using identity: (am × an = am + n)


=


Using identity (am an = am - n)


= 37 - 7


= 3o


= 1


(vi) In the above question,


We have to simplify the given numbers into exponential form:


∴ We have,


20 + 30 + 40


= 1 + 1 + 1


= 3


(vii) In the above question,


We have to simplify the given numbers into exponential form:


∴ We have,


20 × 30 × 40


= 1 × 1 × 1


= 1


(viii) In the above question,


We have to simplify the given numbers into exponential form:


∴ We have,


(30 + 20) × 50


= (1 + 1) × 1


= 2


(ix) In the above question,


We have to simplify the given numbers into exponential form:


∴ We have,



=


Using identity: (am)n = amn



Using identity: (am an = am - n)


= 28 – 6 × a5 - 3


= 22 × a2


Using identity [am ×bm = (a × b)m]


= (2 × a)2


= (2a)2


(x) In the above question,


We have to simplify the given numbers into exponential form:


∴ We have,


() × a8


Using identity: (am an = am - n)


= a5 – 3 × a8


= a2 × a8


Using identity (am × an = am + n)


= a2 + 8


= a10


(xi) In the above question,


We have to simplify the given numbers into exponential form:


∴ We have,



Using identity: (am an = am - n)


= 45 – 5 × a8 – 5 × b3 – 2


= 40 × a3 × b1


= 1 × a3 × b


= a3b


(xii) In the above question,


We have to simplify the given numbers into exponential form:


∴ We have,


(23 × 2)2


Using identity: (am × an = am + n)


= (23 + 1)2


= (24)2


Using identity: (am)n = amn


Therefore,


= 24 × 2


= 28


Question 3.

Say true or false and justify your answer:

(i) 10 × 1011 = 10011

(ii) 23 > 52

(iii) 23 × 32 = 65

(iv) 30 = (1000)0


Answer:

(i) We have,

10 × 1011 = 10011


L.H.S. = 10 × 1011


Using identity: (am × an = am + n)


= 1011 + 1


= 1012


R.H.S. = 10011


= (10 × 10)11


= (102)11


Using identity: (am)n = amn


= 102 × 11


= 1022


So, it is clear that


L.H.S. R.H.S.


∴ The statement given in the question is false


(ii) We have,


23 > 52


L.H.S. = 23


= 2 × 2 × 2


= 8


R.H.S. = 52


= 5 × 5


= 25


Since,


It is clear that 25 > 8


∴ The statement given in the question is false


(iii) We have,


23 × 32 = 65


L.H.S. = 23 × 32


= 2 × 2 × 2 × 3 × 3


= 72


R.H.S. = 65


= 6 × 6 × 6 × 6 × 6


= 7776


It is clear that


L.H.S. R.H.S.


∴ The statement given in the question is false


(iv) We have,


30 = (1000)0


L.H.S. = 30


= 1


R.H.S. = (1000)0


= 1


Hence,


L.H.S. = R.H.S.


∴ The statement given in the question is true


Question 4.

Express each of the following as a product of prime factors only in exponential form:

(i) 108 × 192

(ii) 270

(iii) 729 × 64

(iv) 768


Answer:

(i) We have,

108 × 192


We have to express this as a product of prime factors only in exponential form


∴ 108 × 192


= (2 × 2 × 3 × 3 × 3) × (2 × 2 × 2 × 2 × 2 × 2 × 3)


= (22 × 33) × (26 × 3)


Using identity: (am × an = am + n)


= 26 + 2 × 33 + 1


= 28 × 34


(ii) We have,


270


We have to express this as a product of prime factors only in exponential form


Thus,


270


= 2 × 3 × 3 × 3 × 5


= 2 × 33 × 5


(iii) We have,


729 × 64


We have to express this as a product of prime factors only in exponential form


Thus,


729 × 64


= (3 × 3 × 3 × 3 × 3 × 3) × (2 × 2 × 2 × 2 × 2 × 2)


= 36 × 26


(iv) We have,


768


We have to express this as a product of prime factors only in exponential form


Thus, 768 = 2 × 2 × 2 × 2 × 2 × 2 × 2 × 2 × 3


= 28 × 3



Question 5.

Simplify:

(i)

(ii)

(iii)


Answer:

(i)

We have,

Using identity: (am)n = amn , we get,


Using identity: (am)n = amn, we get,


=


Using identity: (am an = am - n)


= 210 - 9 × 73 – 1


= 21 × 72


= 2 × 7 × 7


= 98


(ii) We have,



Using identity: [(a × b)m = am ×bm]



Using identity: (am × an = am + n)


=


By using (am an = am - n), we get:


=


=


(iii) We have,



=


Using identity: [(a × b)m = am ×bm]


=


Using identity: (am × an = am + n)



By using (am an = am - n), we get:


= 35 – 5 × 25 – 5 × 57 – 7


= 30 × 20 × 50


= 1 × 1 × 1


= 1



Exercise 13.3
Question 1.

Write the following numbers in the expanded forms:

279404, 3006194, 2806196, 120719, 20068


Answer:

In this question,

We have to write the above given numbers into expanded form:


∴ 279404 = 2 × 105 + 7 × 104 + 9 × 103 + 4 × 102 + 0 × 101 + 4 × 100


3006194 = 3 × 106 + 0 × 105 + 0 × 104 + 6 × 103 + 1 × 102 + 9 × 101 + 4 × 100


2806196 = 2 × 106 + 8 × 105 + 0 × 104 + 6 × 103 + 1 × 102 + 9 × 101 + 6 × 100


120719 = 1 × 105 + 2 × 104 + 0 × 103 + 7 × 102 + 1 × 101 + 9 × 100


20068 = 2 × 104 + 0 × 103 + 0 × 102 + 6 × 101 + 8 × 100


Question 2.

Find the number from each of the following expanded form:

(a) 8 × 104 + 6 × 103 + 0 × 102 + 4 × 101 + 5 × 100

(b) 4 × 105 + 5 × 103 + 3 × 102 + 2 × 100

(c) 3 × 104 + 7 × 102 + 5 × 100

(d) 9 × 105 + 2 × 102 + 3 × 101


Answer:

(a) In this question,

We have to find the number from above given numbers which are in expanded form:


Thus,


8 × 104 + 6 × 103 + 0 × 102 + 4 × 101 + 5 × 100


= 80000 + 6000 + 00 + 40 + 5


= 86045


(b) In this question,


We have to find the number from above given numbers which are in expanded form:


Thus,


4 × 105 + 5 × 103 + 3 × 102 + 2 × 100


= 400000 + 5000 + 300 + 2


= 405302


(c) In this question,


We have to find the number from above given numbers which are in expanded form:


Thus,


3 × 104 + 7 × 102 + 5 × 100


= 30000 + 700 + 5


= 30705


(d) In this question,


We have to find the number from above given numbers which are in expanded form:


Thus,


9 × 105 + 2 × 102 + 3 × 101


= 900000 + 200 + 30


= 900230



Question 3.

Express the following numbers in standard form:

(i) 5, 00, 00, 000

(ii) 70, 00, 000

(iii) 3, 18, 65, 00, 000

(iv) 3, 90, 878

(v) 3, 9087.8

(vi) 3908.78


Answer:

(i) We have to express the given number in standard form:

Thus,


5, 00, 00, 000 = 5 × 107


(ii) We have to express the given number in standard form:


Thus,


70, 00, 000 = 7 × 106


(iii) We have to express the given number in standard form:


Thus,


3, 18, 65, 00, 000 = 3.1865 × 109


(iv) We have to express the given number in standard form:


Thus,


3, 90, 878 = 3.90878 × 105


(v) We have to express the given number in standard form:


Thus,


39087.8 = 3.90878 × 104


(vi) We have to express the given number into the standard form:


Thus,


3908.78 = 3.90879 × 103



Question 4.

Express the number appearing in the following statements in standard form.

(a) The distance between Earth and Moon is 384,000,000 m.

(b) Speed of light in vacuum is 300,000,000 m/s.

(c) Diameter of the Earth is 1,27,56,000 m.

(d) Diameter of the Sun is 1,400,000,000 m.

(e) In a galaxy there are on an average 100,000,000,000 stars.

(f) The universe is estimated to be about 12,000,000,000 years old.

(g) The distance of the Sun form the centre of the Milky Way Galaxy is estimated to be 300,000,000,000,000,000,000 gm.

(h) 60,230, 000,000,000,000,000,000 molecules are contained in a drop of water weighting 1.8 gm.

(i) The earth has 1,353,000,000 cubic km of sea water.

(j) The population of India was about 1,027,000,000 in March, 2001


Answer:

(a) It is given that,

Distance between Earth and Moon = 384, 000, 000 m


Thus,


384, 000, 000 = 3.84 × 108 m


(b) It is given that,


Speed of light in vacuum = 300, 000, 000 m/s


Thus,


300, 000, 000 = 3 × 108 m/s


(c)It is given that,


Diameter of Earth = 1, 27, 56, 000 m


Thus,


1, 27, 56, 000 = 1.2756 × 107 m


(d) It is given that,


Diameter of Sun = 1, 400, 000, 000 m


Thus,


1, 400, 000, 000 = 1.4 × 109 m


(e) It is given that,


Average number of stars in galaxy = 100, 000, 000, 000 stars


Thus,


100, 000, 000, 000 = 1 × 1011 stars


(f) It is given that,


Estimated age of universal = 12, 000, 000, 000 years


Thus,


12, 000, 000, 000 = 1.2 × 1010 years


(g) It is given that,


Distance of sun from the centre of Milky Way galaxy = 300, 000, 000, 000, 000, 000, 000 m


Thus,


300, 000, 000, 000, 000, 000, 000 = 3 × 1020 m


(h) It is given that,


Total number of molecules in a drop of water weighing 1.8 gram = 60, 230, 000, 000, 000, 000, 000, 000 m


Thus,


60, 230, 000, 000, 000, 000, 000, 000 = 6.023 × 1022


(i) It is given that,


Area of sea water on earth = 1, 353, 000, 000 cubic km


Thus,


1, 353, 000, 000 = 1.353 × 109 cubic km


(j) It is given that,


Population of India in March 2001= 1, 027, 000, 000


Thus,


1, 027, 000, 000 = 1.027 × 109