Exponents and Powers - Solutions 2

CBSE Class –VIII Mathematics
NCERT Solutions
CHAPTER - 12
Exponents and Powers (Ex. 12.2)

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1. Express the following numbers in standard form:

(i) 0.0000000000085

(ii) 0.00000000000942

(iii) 6020000000000000

(iv) 0.00000000837

(v) 31860000000

Ans. (i) 0.0000000000085

= 0.0000000000085   = 

(ii) 0.00000000000942

= 0.00000000000942   =

(iii) 6020000000000000

= 6020000000000000   = 

(iv) 0.00000000837

= 0.00000000837   = 

(v) 31860000000

= 31860000000   = 

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2. Express the following numbers in usual form:

(i) 

(ii) 

(iii) 

(iv) 

(v) 

(vi) 

Ans. (i) $$

(ii) 4.5  10000 = 45000

(iii)  = 0.00000003

(iv)  = 1000100000

(v)  = 5.8 x 1000000000000

= 5800000000000

(vi)  = 3.61492  1000000

= 3614920

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

(i)1 micron is equal to  m.

(ii) Charge of an electron is 0.000,000,000,000,000,000,16 coulomb.

(iii) Size of a bacteria is 0.0000005 m.

(iv) Size of a plant cell is

0.00001275 m.

(v) Thickness if a thick paper is 0.07 mm.

Ans. (i) 1 micron

=  m

(ii)Charge of an electron is

0.00000000000000000016 coulombs.

=0.00000000000000000016×10191019$0.00000000000000000016\times \frac{{10}^{19}}{{10}^{19}}$

=  coulomb

(iii) Size of bacteria = 0.0000005

510000000=5107=5×10−7$\frac{5}{10000000}=\frac{5}{10^7}=5\times 10^{-7}$ m

(iv) Size of a plant cell is 0.00001275 m

= 0.00001275   =  m

(v) Thickness of a thick paper = 0.07 mm

= mm =  mm

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4. In a stack there are 5 books each of thickness 20 mm and 5 paper sheets each of thickness 0.016 mm. What is the total thickness of the stack?

Ans. Thickness of one book = 20 mm

Thickness of 5 books = 20  5 = 100 mm

Thickness of one paper = 0.016 mm

Thickness of 5 papers = 0.016  5

= 0.08 mm

Total thickness of a stack = 100 + 0.08

=100.08 mm

= 100.08 

 mm