this has to do the adding/subtracting signs...
when u r adding/subtracting signs....if the signs are the same, u add them and keep the sign.
-4 + (-2) = -4 - 2 = -6...........2 + 5 = 7......-3 + (-1) = -3 - 1 = -4
when ur adding/subtracting signs...if the signs are different, u subtract and take the sign of the larger number...
-4 + 7......subtract 7 - 4 = 3....the larger number (7) is positive, so ur answer is positive....so ur answer is 3
4 - 7....subtract 7 - 4 = 3....the larger number(-7) is negative, so ur answer is negative.....ur answer is -3
but dont get this confused with multiplying/dividing with signs....they have different rules