Summarize:

Adding a negative integer is the same as subtracting a positive one. This is easier to see by testing this out with the number line method described in another section, but you can think about it in words too. A negative number is not a normal quantity; it is less than zero, and can represent an amount being taken away. If you add this "taking away" to a normal number, you'll end up making it smaller.  Example: 10 + -3 = 10 - 3 = 7 Example: -12 + 18 = 18 + -12 = 18 – 12 = 6. Remember that you can always switch the order of numbers in an addition problem, but not in a subtraction problem. Sometimes turning your addition problem into a subtraction problem  as described above can end up with odd results like 4 – 7. When this happens, reverse the order of the numbers and make your answer negative.  Say you begin with 4 + -7. Turn this into a subtraction problem: 4 - 7 Reverse the order and make it negative: -(7 – 4) = -(3) = -3. If you aren't used to parentheses in your equations yet, think of it like this: 4 - 7 turns into 7 - 4 with a minus sign added. 7 - 4 = 3 but I should make it -3 for the right answer to the problem 4 - 7. Two negative numbers added together will always make a number more negative. There is nothing positive being added, so you'll always end up with something further from 0. Finding the answer is simple:  -3 + -6 = -9 -15 + -5 = -20 Do you see the pattern? All you need to do is add the numbers as though they were positive and add a negative sign. -4 + -3 = -(4 + 3) = -7 Just like the addition problems, you can rewrite these so you only have to deal with positive numbers. If you're subtracting a negative number, you're "taking away" some "stuff taken away", which is the same as adding a positive number.  Think of the negative number as stolen money. If you "subtract", or take away, some stolen money so you can return it, that's the same as giving that person money, right? Example: 10 – -5 = 10 + 5 = 15 Example: -1 – -2 = -1 + 2. You already learned how to solve this problem in an early step, remember? Reread Learn how to add a negative and a positive number if you don't remember. Here's the full solution to the last example: -1 – -2 = -1 + 2 = 2 + -1 = 2 – 1 = 1.
Learn how to add a negative and a positive number. Learn what to do if this turns into a subtraction problem with a smaller number first. Learn how to add two negative integers. Learn how to subtract a negative integer.