I need a good explination to understand why a positive number minus a negative number equals a positive or in other words you add it.

ex 10-(-5)= 15

eliminate parenthesis:

(+)(+)= +
(-)(-)= +
(+)(-)= -
(-)(+)= -
same signs ---> postive.
dif. signs ---> negative.

ex. 3+(-1)
3-1 =3 cause +&- means to subtract,so the negative 1 comvert into positive 1& you subtract it.Hope it helps you. >;D