Question

Explain how you know whether a sum is positive,negative,or zero without actually adding

Answer 1

Example: -8 - (-9)
if there is 2 negative signs on the inside then you change it to a plus.
-8 + 9 
because the 9 is bigger than 8 you switch.
9 - 8
answer is 1

Answer 2

When you're summing two numbers . . .

-- The sum is positive if the bigger one is positive.
(Then it doesn't matter what the sign of the other one is.)

-- The sum is negative if the bigger one is negative.
(Then it doesn't matter what the sign of the other one is.)

-- The sum is zero if both numbers are zero,
or
   the numbers have the same absolute value but different signs.