## MP Board Class 8th Maths Solutions Chapter 12 Exponents and Powers Ex 12.2

Question 1.

Express the following numbers in standard form.

(i) 0.0000000000085

(ii) 0.00000000000942

(iii) 6020000000000000

(iv) 0.00000000837

(v) 31860000000

Solution:

(i) 0.0000000000085 = 8.5 × 10^{-12}

(ii) 0.00000000000942 = 9.42 × 10^{-12}

(iii) 6020000000000000 = 6.02 × 10^{15}

(iv) 0.00000000837 = 8.37 × 10^{-9}

(v) 31860000000 = 3.186 × 10^{10}

Question 2.

Express the following numbers in usual form.

(i) 3.02 × 10^{-6}

(ii) 4.5 × 10^{4}

(iii) 3 × 10^{-8}

(iv) 1.0001 × 10^{9}

(v) 5.8 × 10^{12}

(vi) 3.61492 × 10^{6}

Solution:

(i) We have, 3.02 × 10^{-6} = 0.00000302

(ii) We have, 4.5 × 10^{4} = 45000

(iii) We have, 3 × 10^{-8} = 0.00000003

(iv) We have, 1.0001 × 10^{9} = 1000100000

(v) We have, 5.8 × 10^{12} = 5800000000000

(vi) We have, 3.61492 × 10^{6} = 3614920

Question 3.

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

(i) 1 micron is equal to \(\frac{1}{1000000}\) 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 of a thick paper is 0.07 mm.

Solution:

(i) Standard form of given statement = 1 × 10^{-8}.

(ii) Standard form of given statement = 1.6 × 10^{-19}.

(iii) Standard form of given statement = 5 × 10^{-7}.

(iv) Standard form of given statement = 1.275 × 10^{-5}.

(v) Standard form of given statement = 7 × 10^{-2}.

Question 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.

Solution:

Total number of books = 5

Thickness of each book = 20 mm

∴ Thickness of 5 books = (5 × 20) mm = 100 mm

Thickness of each paper sheet = 0.016 mm

∴ Thickness of 5 paper sheets = (5 × 0.016) mm = 0.08 mm

Hence, total thickness of stack = 100 mm + 0.08 mm

= 100.08 mm = 1.0008 × 10^{2} mm