Rule 1 Addition of two Numbers with the same sign The result is the sum of the numbers with the given sign ( the sign of the two numbers ) .
Situation 1: ++ =+
When we add two plus numbers we get a plus number
Ex : 3+6=9.
Situation 2: – – =+
When we add two minus numbers we get a minus number but the value of the answer is more than the two additives that’s why its Plus sign
Ex : -5 + – 6 = – 11 .
Example 5 + 6 + 8 = 19 . Example -5 + – 8 + – 6 = – 19 .
Rule 2 : Addition of two numbers with different signs the result is the difference between the numbers with the sign of the” bigger number ” .
Situation 3: – + = –
Ex 6 + – 9 = – 3 : Ex 19 + -5 = 14 . Ex -15 + 13 = – 2 .
In the above example the answer is decreasing therefore negative sign applies.
Note Ex : 14 – 9 is the same as 14 + – 9 = 5 . and – 7 – 5 is really -7 + – 5 = – 12
Example simplify – 6 + 9 – 7 + 3 + 6 – 8 = – 6 – 7 – 8 + 9 + 3 + 6 = – 21 + 18 = – 3 .
Note we add the minus numbers ,we add the plus numbers then tidy it up .
Rule 3 : Multiplication and signs :
The basic rules for multiplication and signs are as follows
(Minus ) x ( Minus ) = Plus . ( Minus ) x ( Plus ) = Minus , (Plus ) x (Plus ) = Plus .
This can be expressed as follows that
(a) when we multiply two numbers with the same sign we get plus
( b) when we multiply two numbers with difference signs we get a minus .
Example : – 7 x – 5 = + 35 , -7 x 5 = -35 . Example – 7. x – 4 x 3 = 28 x 3 = 84 .
Brainstorming Questions: Can you tell why in the above conditions of rule 3 results are like that
Note: if we are asked to multiply three or more numbers remember you can only multiply two numbers at a time .
Example – 4 x -3 x 5 x -2 = 12 x 5 x – 2 = 60 . x – 2 = – 120 .