I found my LCD, now what?

Step 2: I found my LCD, now what?

Now we need to change our denominators to the LCD. In our example we already have one example over 15 (6/15). So, now we just have to set our other fraction (4/5) to be over 15. To do this we have to figure out what number we must multiple the denominator by to get our LCD. In terms of an algebraic expression for our equation it would be: 5x=15; solving for x. Assuming you know how to handle an equation this is very easy. Divide both sides by 5 to get x = 3. Now that we know what we need to multiple the denominator by to get to the LCD we must multiply the numerator by that number also.

4/5 * 3/3 = 12/15
_{for help on multiplying fractions see step 3 of this instructable by meeze}

Why can we do this? Wouldn't that change the equation?
No.
If the numerator and the denominator are the same it is equivalent to one (1). As we all know multiplying anything by one causes the number to stay the same.