Back to adding signed numbers

Rules for subtracting signed numbers:

We subtract signed numbers by changing the problem to addition. We do this by changing the sign of the second number.
    Step 1:   Change the sign of the second number to its opposite.
    Step 2:   Change the operation to addition.
    Step 3:   Follow the rules for adding signed numbers.
 
Examples:
   +3 - -7 =
step 1    change the sign of the 2nd number    +3 - +7 =

step 2    change the operation to addition      +3 + +7 =

step 3     follow addition rules (now they're the same sign)
        +3 + +7 = +10

   -3 - -7 =
step 1    change the sign of the 2nd number    -3 - +7 =

step 2    change the operation to addition      -3 + +7 =

step 3     follow addition rules (now they're the same sign)
    -3 + +7 = +4