8's friend is 125 as $8\times 125=1000$

$\frac{1}{8}\times \frac{125}{125}=\frac{125}{1000}=0.125$

We have to do the addition.
$500+4+\frac{4}{100}=500+4+0.04$
$500+4+0.04\underset{–}{\overline{504.04}}$
$\therefore$ $500+4+\frac{4}{100}=504.04$

Given:

$24\times 16=384$

Since 24 got divided by 10 to give 2.4, similarly 384 will also be divided by 10 to yeild 38.4

$\therefore 2.4\times 16$= $38.4$

Given: Cost of 1 pencil = ₹ 5.75

$\therefore$ Cost of 100 pencils $=\text{₹}(5.75\times 100)$
$\Rightarrow$ Cost of 100 pencils = ₹ 575

To find the other number, we have to subtract 2.75 from 10.

$09910\text{/}1\text{/}0.\text{/}0\text{/}0-\underset{–}{2.75}\underset{–}{7.25}$ 
 

$\frac{8}{0.2}\times \frac{10}{10}=\frac{80}{2}=40$

Any number multiplied by 0 gives 0 as a result. 

So, $0.9\times 0.83\times 0.75\times 0=0$

$0.9\times 0.9=\frac{9}{10}\times \frac{9}{10}$

=> $0.9\times 0.9$ = $\frac{81}{100}$

=> $0.9\times 0.9$ = $0.81$

We have to find the unknown value which gets multiplied by 0.389 and gives 38.9

$\to$ $0.389\times x$ = $38.9$

=> $x$ = $38.9÷0.389$

=> $x$ = $\frac{38.9}{0.389}$

=> $x$ = $100$