# NCERT Solution For Class 8 Math Chapter –  Exponents and Power  Exercise – 12.2

Q1. Express the following numbers into standard form.

• 0000000000085
• 00000000000942
• 6020000000000000
• 00000000837
• 31860000000

Solution:-

(i)

= 0.0000000000085 x (1012 / 1012) = 8.5 x 10-12

(ii)

= 0.00000000000942 x (1012/1012) = 9.42 x 10-12

(iii)

=  6020000000000000 x (1015/1015) = 6.02 x 1015

(iv)

= 0.00000000837 x (109/109) = 8.37 x 10-9

(v)

= 31860000000 x (1010 / 1010) = 3.186 x 1010

Q2. Express the following numbers in usual form.

• 02 x 10-6
• 5 x 104
• 3 x 10-8
• 001 x 109
• 8 x 1012
• 61492 x 106

Solution:-

(i)

= 3.02/106 = 0.00000302

(ii)

= 4.5 x 10000 = 450000

(iii)

= 3/108 = 0.00000003

(iv)

= 5.8  x 100000000000 = 58000000000000

(v)

= 3.61492 x 1000000 =

3614920

(vi)

=  1000100000

Q3. Express the number appearing in the following statements in standard form.

• 1 micron is equal to 1/1000000 m.
• Charge of an electron is 0.000 , 000 , 000 , 000 , 000 , 000 , 16 coulomb.
• Size of bacteria is 0.0000005 m
• Size of a plant cell is 0.00001275 m.
• Thickness of a thick paper is 0.07 mm.

Solution:-

• 1 micron = 1/1000000

= 1/106

= 1 x 10-6

• Charge of an electron is 0.00000000000000000016 coulombs.

= 0.00000000000000000016 x 1019 / 1019

= 1.6 x 10-19 coulomb

• Size of bacteria = 0.0000005

5/10000000 – 5/107 = 5 x 10-7 m

• Size of a plant cells 0.00001275 m

= 0.0000001275 x 105/105

= 1.275 x 10-5 m

• Thickness of a thick paper = 0.07 mm

0.07 mm = 7/100 mm = 7/102 = 7 x 10-2 mm

Q4. 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 ?

Solution:-

Thickness of one books = 20 mm

Thickness of 5 books = 20 x 5 = 100 mm

Thickness of paper = 0.016 mm

Thickness of 5 papers = 0.016 x 5 = 0.08

Total thickness of a stack = 100 + 0.08 = 100.08 mm

= 100.08 x 102/102 mm

= 1.0008 x 102 mm