Explain negative numbers - how it works when you +, -, x and divide. !

Negative/negative=Positive (they cancel out)
negative/Positive=negative
negative X negative = Positive (they cancel out)
negative X Positive = Negative
when adding the negatives will not cancel. If the negative number is bigger the it will = a negative and Viceversa 

Take note:  
i) Negative +  Negative =  -(Add the two numbers)
Example:  
 -10 + -3  =  - (10+3)
               = -13.
Therefore:    -8 + -3 = -11.  ( Just add the two numbers and put the minus sign).

ii) Small number - Big number = - (big number - small number).
Example:
3 - 5    =   - (5-3)
          = -2.  (just subtract the small number from the big number and add the minus sign)

Example:  1 -7 = -6.  Using same logic.

If gravity is one third on mars then weight also one third on mars