A product of two integers can be positive or negative or zero.
Example:  
   $5\times 6=30$ or    
$-5\times (-6)=30$, 
   $5\times (-4)=-20$,
   $5\times 0=0$

Let x be the integer to be found.​

$x\times (-13)$ = -143

x = $\frac{-143}{-13}$ = 11

Here, 
$(1-2)=-(2-1)=-1$ 
 $(3-4)=-(4-3)=-1$
   .
   .   
 $(19-20)=-(20-19)=-1$. 

There are 10 pairs having a value -1.

$\therefore 1-2+3-4+5-6+...........+19-20$
$=+10\times (-1)=-10[\because x\times (-y)=-xy]$

For any integer a, a ÷ 0 is not defined.
We know that, division is a repeated subtraction.
For example 15÷3 is  
15-3 = 12
12-3 = 9
9-3 = 6
6-3 = 3
3-3 = 0
Therefore, 15÷3 = 5.
Similarly 15 ÷ 0 is
15 - 0 = 15
15 - 0 = 15
15 - 0 = 15
15 - 0 = 15  and so on ...
Therefore, division of an integer by 0 is not defined.

If 'a' and 'b' are any two integers, then by associative property;

a+(b+c) = (a+b)+c

LHS = 
8+ (-13) - 15 = 8 + (-28) = -20
RHS = 
-15 + (-39) + 6 = -54 + 6 = -48
-20  $>$ -48
$\therefore$ 8+ (-13) - 15  is greater than -15 -39 + 6

$\frac{-2}{\left(2\right)}=-1\ne -4$ ​​​​​​​
$\frac{8}{(-2)}=-4$ ​​​​​​​​​​​​​​
$\frac{-4}{\left(2\right)}=-2\ne -4$ ​​​​​​​​​​​​​​
$\frac{4}{\left(1\right)}=4\ne -4$ ​​​​​​​​​​​​​​
$\therefore$ (8, -2) is the required pair.

-6 + 7= 1

1 - (-8) = 1 + 8 = 9

Stand on -6 on the number line, then move 7 places to the right in order to add 7 to -6. You will reach 1.

Now, move 8 places to the right to subtract -8 from 1. You will reach 9 i.e.1-(-8) = 1 + 8 = 9

Here,
Sum of 883 and -479

= 883 + (-479) = 883 - 479
= 404

Now, subtracting the sum from -76 
= -76 - 404 
= -480

The additive inverse of a number 'x' is the number that, which when added to 'x' results in zero.

 -55 + 55 = 0. Therefore, additive inverse of -55 is 55.