Ncert Solutions For Class 8 Maths Ex 12.2

Ncert Solutions For Class 8 Maths Chapter 12 Ex 12.2

Q.1. Converts the numbers into standard form:

(i)0.0000000000085

(ii)0.00000000000942

(iii)6020000000000000

(iv)0.00000000837

(v)31860000000

 

Solution:

(i)0.0000000000085

0.0000000000085=0.0000000000085×10121012=8.5×1012

 

(ii)0.00000000000942

0.00000000000942=0.00000000000942×10121012=9.42×1012

 

(iii)6020000000000000

6020000000000000=6020000000000000×10151015=6.02×1015

 

(iv)0.00000000837

0.00000000837=0.00000000837×109109=8.37×109

 

(v)31860000000

31860000000=31860000000×10101010=3.186×1010

 

Q.2. Convert the following numbers in usual form:

(i)3.02×106

(ii)4.5×104

(iii)3×108

(iv)1.0001×109

(v) 5.8×1012

(vi)3.61492×106

 

Solution:

(i)3.02×106

3.02×106=3.02106=0.00000302

 

(ii)4.5×104

4.5×104=4.5×10000=45000

 

(iii) 3×108

3×108=3108=0.00000003

 

(iv) 1.0001×109

1.0001×109=1000100000

 

(v) 5.8×1012

5.8×1012=5.8×1000000000000=5800000000000

 

(vi) 3.61492×106

3.61492×106=3.61492×1000000=3614920

 

Q.3. Conert the given numbers in the following statements in standard form:

(i) 1 micron is equal to 11000000 m.

(ii)Charge of an electron is 0.000,000,000,000,000,000,28 coulomb.

(iii)Size of 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.

 

Solution:

(i)1 micron =11000000=1106=1×106m

 

(ii) Charge of an electron is 0.00000000000000000028 coulombs.

=0.00000000000000000028×10191019=2.8×1019coulomb

 

(iii)Size of bacteria = 0.0000005 =510000000=5107=5×107m

 

(iv)Size of a plant cell is 0.00001275 m =0.00001275×105105=1.275×105m

 

(v) Thickness of a thick paper = 0.07 mm =7100mm=7102=7×102mm

 

Q.4. In a stack there are 6 books each of thickness 20 mm and 5 paper sheets each of thickness 0.016 mm. What is the total thickness of the stack?

Solution:

Thickness of one book = 20 mm

Thickness of 6 books =20×6=120mm

Thickness of one paper = 0.016 mm

Thickness of 5 papers =0.016×5=0.08mm

Total thickness of a stack =120+0.08

=120.08 mm=120.08×102102=1.2008×102mm

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