SMART MATH Calculate The Numbers Round Operation 
a. Summation with tools.

In calculating the sum of two integers, can used by using the number line. Numbers are summed illustrated with arrows corresponding to the direction with the number.If the positive numbers, arrows pointing the right direction. Conversely, if the negative number, the arrows pointing in the direction of left. 
1. 6 + (-8) 
2. (-3) + (-4) 

b. Summation without tools 
The sum of the numbers of little value can be done with the help of a number line. However, for the numbers of great value, it can not be done. Therefore,we should be able to add up the integers without tools.1) Both numbers marked with the same.

If both marked with the same numbers (both numbers positive or both negative numbers), totalizing both numbers. The result is the same mark with the mark the two numbers. 

SMART MATH Calculate The Numbers Round Operation

Example: 

a) 125 + 234 = 359

b) -58 + (-72) = - (58 + 72) = -1302) 

The two numbers opposite sign.

If the two numbers opposite sign (positive numbers and negative numbers), reduce the number of greater value with a smaller number of value without notice sign. The result, according tick numbers are worth greater.
 

SMART MATH Calculate The Numbers Round Operation

Example: 

a) 75 + (-90) = - (90-75) = -15
b) (-63) + 125 = 125-63 = 62
a. 6 + 5 = 5 + 6 = 11
b. (-7) + 4 = 4 + (-7) = -3
c. 8 + (-12) = (-12) + 8 = -4
d. (-9) + (-11) = (-11) + (-9) = -20

c.Has the identity element.

Number 0 (zero) is the identity element in summation. That is, for any integer when added to 0 (zero), the result is the number itself. It can be written as follows. For any integers a, always applya + 0 = 0 + a = a.

 d.Associative properties.

Associative properties of nature also called grouping. This trait can be written as follows.For any integers a, b, and c, apply(A + b) + c = a + (b + c).  

Properties Integer Additiona.Closed nature,On the sum of integers, always produces integers as well. It can be written as follows. For any integers a and b, apply a + b = cwith c is also an integer. 

a. -16 + 25 = 9-16 And 25 are integers.9 is also an integer. 

b. 24 + (-8) = 1624 and -8 are integers.16 is also an integer. 

b.Commutative propertiesCommutative properties called exchange properties. Addition two integers always obtained the same results although both numbers are exchanged place. It can be written as follows.For any integers a and b, always apply 

a + b = b + a.
 a. 6 + 5 = 5 + 6 = 11 
b. (-7) + 4 = 4 + (-7) = -3 
c. 8 + (-12) = (-12) + 8 = -4 
d. (-9) + (-11) = (-11) + (-9) = -20c. 

Has the identity element Number 0 (zero) is the identity element in summation. That is, for any integer when added to 0 (zero), the result is the number itself.It can be written as follows.For any integers a, always apply a + 0 = 0 + a = a.d.Associative properties Associative properties of nature also called grouping. This trait can be written as follows.For any integers a, b, and c, apply(A + b) + c = a + (b + c).

For a more Formula Math here