One of the most basic skills (and the one that will get you through every upper level math) is the ability to solve for a missing number in any equation.
The key to finding a missing number is to undo every operation in the sentence. What does that mean? Basically, it means that you’re going to add where you see subtraction (or vice versa) and multiply where you see division (or vice versa).
For example, let’s solve for x in the following equation:
3x – 6 = 9
The first step we need to do is group all of the non-x terms on the same side of the equation. To do that, we add 6 to both sides of the equation. We add it to the left side to cancel it from that side, and we add it to the right side to keep our equation balanced. The result looks like this:
3x = 15
Remember that 3x is the same as saying 3 * x, so we can now divide both sides by 3. Again, we divide the left side by 3 to cancel it from that side, and we divide the right side by three to keep our equation balanced. This leaves us with:
x = 5
We now know the value of the variable.
The most important thing to remember when solving for a variable is that we need to group like terms so the variable we’re solving for ends up alone on one side of the equation. This makes it possible for us to find the value of that variable.
