negative 8 minus positive 9

Answer 1

I want you to grab a sheet of paper and make a number line. This is a horizontal line, and in the middle you should mark zero.

__________0___________

Now go ahead and make 10 dashes on either side of that zero and number them, with the 1 being closest to the zero and the 20 as the farthest dash. (I'm going to line these up as best I can, but it may not be perfect on my end due to font, and I'm only going to go to ten on here. You'll still get the idea).

|__|__|__|__|__|__|__|__|__|__0__|__|__|__|__|__|__|__|__|__|

10 9 8 7 6 5 4 3 2 1 1 2 3 4 5 6 7 8 9 10

The left hand side of your line is the negative side, while the the numbers to the right of that zero are positive.

When we subtract, regardless of the sign of what we are removing from our first number, we go left. To add, we go right. For example, say we want to know what -1 - 3 is. Find your -1 (remember it's to the left of zero). Now, NOT counting the -1, count 3 to the left of it. This means you start counting at -2, which would be 1 in your count, -3 would be 2, and -4 would be three.

-1 -3 = -4.

What if we are adding 3 to -1? Same thing, only counting to the right. We start at 0 (1 in our count), then 1, then 2 (which makes 3 away from -1).

-1 + 3 = 2

Now try it with your problem. Make a number line that goes up to 20, and count 9 to the left of -8.

Let me know if this helps, or if we need to do another example. I can also show you some shortcuts if you feel comfortable.