## Standard Form

A number written as ( m x $$10^n$$ ) is said to be in standard form if m is a decimal number such that 1 $$\le$$ m $$<$$10 and n is either a positive or a negative integer.

The standard form of a number is also known as Scientific notation.

## Expressing Very Large Numbers in Standard Form

In order to write large numbers in the standard form,following steps must be followed:

STEP I– Obtain the number and move the decimal point to the left till you get just one digit to the left of the decimal point.

STEP II– Write the given number as the product of the number so obtained and $$10^n$$ , where n is the number of places the decimal point has been moved to the left. If the given number is between 1 and 10, then write it as the product of the number itself and $$10^0$$ .

Illustrative Examples

Example 1: Express the following numbers in the standard form:

(i) 3,90,878    (ii) 3,186,500,000    (iii) 65,950,000

Solution.

(i) We have,

3,90,878 = 390878.00
Clearly, the decimal point is moved through five places to obtain a number in which there is just one digit to the left of the decimal point.

Therefore,    390878.00 = 3.90878 x $$10^5$$

(ii) We have,

3,186,500,000 = 3.186500000 x $$10^9$$
= 3.1865 x $$10^9$$
(iii) We have,

65,950,000 = 65,950,000.00

= 6.5950000 x $$10^7$$
= 6.595 x $$10^7$$

Example 2: The distance between sun and earth is (1.496 x $${10}^{11}$$) m and the distance between earth and moon is (3.84 x $$10^8$$) m. During solar eclipse moon comes in between earth and sun. At that time what Is the distance between moon and sun?

Solution.    Required distance

= {(1.496 x $${10}^{11}$$) – (3.84 x $$10^8$$) } m

= {$$\frac { 1496\times { 10 }^{ 11 } }{ { 10 }^{ 3 } }$$ – (3.84 x $$10^8$$)} m

= {1496 x $$10^8$$) – (3.84 x $$10^8$$)} m

= {(1496 – 3.84) x $$10^8$$)} m

= (1492.16 x $$10^8$$) m

Hence, the distance between moon and sun is (1492.16 x $$10^8$$ ) m.

Example 3: Write the following numbers in the usual form:

(i) 7.54 x $$10^6$$    (ii)2.514 x $$10^7$$

Solution.    We have

(i) 7.54 x $$10^6$$

= $$\frac{754}{100}$$ x $$10^6$$

= $$\frac{754 \times {10}^{6} }{{10}^{2}}$$

= 754 x $${10}^{(6-2)}$$

= (754 x $${10}^{4}$$ )

= (754 x 10000) = 7540000

(ii) 2.514 x $$10^7$$

= $$\frac{2514}{1000}$$ x $$10^7$$

= $$\frac{2514 \times {10}^{7} }{{10}^{3}}$$

= 2514 x $${10}^{(7-3)}$$

= (2514 x $${10}^{4}$$ )

= (2514 x 10000) = 25140000

## Expressing Very Small Numbers in Standard Form

In order to write very small numbers in the standard form,following steps must be followed:

STEP I- Obtain the number and count the number of decimal values after the decimal point. Consider it as n.

STEP II- Divide the number by $${10}^{n}$$). If the number is between 1 and 10, then write it as the product of the number itself and $${10}^{-n}$$

Example 1: Write the following numbers in the standard form:

(i) 0.000000059    (ii) 0.00000000526
Solution. We may write:

(i)    0.000000059

= $$\frac{59}{{10}^{9}}$$

=  $$\frac{5.9 \times 10}{{10}^{9}}$$

= $$\frac{5.9}{{10}^{8}}$$ = (5.9 x $${10}^{-8}$$)

(ii) 0.00000000526

= $$\frac{526}{{10}^{11}}$$

= $$\frac{5.26 \times 100}{{10}^{11}}$$

= $$\frac{5.26 \times {10}^{2}}{{10}^{11}}$$

= $$\frac{5.26}{{10}^{(11 – 2)}}$$

= $$\frac{5.26}{{10}^{9}}$$ = (5.26 x $${10}^{-9}$$)

Example 2: The size of a red blood cell is 0.000007 m and that of a plant cell Is 0.00001275 m. Show that a red blood cell is half of plant cell in size.

Solution.    We have,

Size of a red blood cell = 0.000007 m = $$\frac{7}{{10}^{6}}$$ m = (7 x $${10}^{-6}$$)

Size of a plant cell

= 0.00001275 m

= $$\frac{1275}{{10}^{8}}$$ m

= $$\frac{1.275 \times {10}^{3}}{{10}^{8}}$$ m

= $$\frac{1.275}{{10}^{(8-3)}}$$ m

= $$\frac{1.275}{{10}^{5}}$$ m = (1.275 x $${10}^{-5}$$) m

$$\frac{Size of a red blood cell}{Size of a plant cell}$$

= $$\frac{7 \times {10}^{-6}}{1.275 \times {10}^{-5}}$$

= $$\frac{7 \times {10}^{-6 + 5}}{1.275}$$

= $$\frac{7 \times {10}^{-1}}{1.275}$$

= $$\frac{7}{1.275 \times 10}$$

= $$\frac{7}{12.75}$$

= $$\frac{7}{13}$$ (nearly)

= $$\frac{1}{2}$$  (approximately)

Therefore,    size of a red blood cell = $$\frac{1}{2}$$ x (size of a plant cell)

Example 3: Express the following numbers in usual form:

(i) 3 x $${10}^{-3}$$    (ii) 2.34 x $${10}^{-4}$$
Solution.    We have,

(i) 3 x $${10}^{-3}$$

=  $$\frac{3}{{10}^{3}}$$

= $$\frac{3}{1000}$$ = 0.003

(ii) 2.34 x $${10}^{-4}$$

= $$\frac{234}{100}$$ x $$\frac{1}{{10}^{4}}$$

= $$\frac{234}{{10}^{2} \times {10}^{4}}$$

= $$\frac{234}{{10}^{6}}$$

= $$\frac{234}{1000000}$$ = 0.000234