Can be easily solved with following formula

a 2 - b 2 = a - b × a + b

= (25.732 - 15.732 ) x (25.732 + 15.732)

=414.64

Here   1 8 in decimal means 8th part in 1.

We know that  1 10 = 0.1

Then,    1 8 = ?

=>  $$\begin{gathered} ? = 1 8 x 0 . 1 1 10 \\ = 0 . 1 x 10 8 \\ = 0 . 5 4 \\ 1 8 = 0 . 125 \end{gathered}$$

3/8 as a Decimal :

In this we should convert the denominator into 10, 100, 1000, 10000, 100000,... to make it simple.

Now to make 8 into 1000, we multiply numerator and denominator with 125

=>  3 x 125 8 x 125 = 375 1000 = 0 . 375

1/10 as a Decimal :

1 divided into 10 parts of each 0.1.

Therefore, 3/8 = 0.375 and 1/10 = 0.1 in decimals.

3/4 divided by 2

= 3/4/2

= 3/4x2

= 3/8.

Hence, 3/4 divided by 2 is equal to 3/8.

Expressing 3/8 as a decimal fraction:

We can convert 3/8 into a decimal fraction by just dividing 3 by 8 or making 3 into 8 parts.

Then, it is 3/8 = 0.375 as a decimal fraction.

Other Method::

3/8 as a Decimal :

In this we should convert the denominator into 10, 100, 1000, 10000, 100000,... to make it simple.

Now to make 8 into 1000, we multiply numerator and denominator with 125

=> (3 x 125)/(8 x 125) = 375/1000 = 0.375.

Here to say which fraction is greater from the given options, the fraction with greater numerator with same denominator or smaller denominator with same numerator.

To find the greater fraction, among the given options, make the denominators same for the options by finding the LCM of all the denominators.

7/12, 9/16, 13/20, 32/80

Now, LCM of 12, 16, 20, 80 = 240.

Then,

140/240, 135/240, 156/240, 96/240

Here 

$$\begin{gathered} 156 240 > 140 240 > 135 240 > 96 240 \\ = > 13 20 > 7 12 > 9 16 > 32 80 \end{gathered}$$

Hence, largest fraction = 13/20.

Given fraction is 3/5

Now, multiply with 2 for numerator and denominator

we get,

3/5 x 2/2 = 6/10

When we divide, 6 with 10, we get 0.6 as quotient.

Hence, 3/5 as a decimal fraction is 0.6.

5/8 = .625, 7/12 = .5833, 3/4 = .75, 13/16 = .8125

So order will be
7/12 < 5/8 < 3/4 < 13/16

To convert a fraction into decimal, just take the number on top which we called the numerator and divide it by the number at the bottom which we called the denominator.

2/3

How it comes :

$2÷3=0$ bring down the decimal point.

$20÷3=6$ and carry the remainder $2$ to make $20$

$20÷3=6$ and carry the remainder $2$ to make $20$

$20÷3=6$ and carry the remainder $2$ to make $20$

etc...

This gives the recurring decimal 0.6666...

If we round off to two decimals , then it becomes 0.67.

Hence, decimal fraction of 2/3 = 0.67.