Learn about Applications of Subtraction Equations Subtraction equations. So in this problem, it states that a science class studying weather discovers that in a recent year, the average wind speed in Memphis, Tennessee was 23 miles per hour. Less than it was in Cape Hatteras, North Carolina. If the average wind speed in Memphis was 88 miles per hour, what was the average wind speed in Cape Hatteras? In this problem, we can use a subtraction equation to solve. In order to do this, our first step is we need to set up our equation. So we need to write an equation. So let’s let w equal or represent the average wind speed in Cape Hatteras because this is what we’re looking for. We don’t know what the average wind speed is so we’re going to put a w in for the wind speed of Cape Hatteras. Now, let’s set up our problem. So we’re going to take the wind speed of Cape Hatteras and we’re going to subtract the difference from that and that will give us the wind speed in Memphis. So now, we have our equation so let’s go ahead and plug everything in. So the wind speed in Cape Hatteras, we don’t know, so we’re going to put a w in for that. Well the difference was 2.3 miles per hour and that’s going to equal the wind speed of Memphis. After we’ve set up our equation, we’re going to isolate the unknown. So the unknown is our variable, so in this problem, the unknown is w. In order to isolate the unknown, we’re going to use inverse operation. So inverse operation is the opposite of the operation we’re using. So since we are subtracting in this problem, addition is the inverse of subtraction. So if you’re subtracting, the inverse operation is addition, it’s the opposite. So what we’re going to do is we are going to add 2.3 to both sides of this equation to isolate it. So here, we’re going to add 2.3 to both sides. So I'm going to take w-2.3+2.3=8.8+2.3. So if -2.3+2.3 is 0, so that gives me the w by itself and 8.8-2.3 is 11.1. So, the wind speed in Cape Hatteras should be 11.1 miles per hour. However before we move on and say this problem is over we always want to check our answer. So to check our answer, what we’re going to do is we’re going to substitute 11.1 for w in our original equation. So I'm going to take my original equation, w-2.3=8.8 and I'm going to substitute 11.1 in for the w. And that should give me 8.8. So 11.1-2.3 is 8.8 which equals 8.8. So since both sides on this equation are equal, the answer is correct. So the average wind speed in Cape Hatteras is 11.1 miles per hour. Things to remember and to keep in mind is that a quantity on the left side of the equal sign is balanced with the quantity on the right side of the equal sign. To solve a subtraction equation, we isolate the unknown. To isolate the unknown, we use inverse operation. So for instance, addition is the inverse of subtraction. Then we add the same number to both sides of the equation.