Adding fractions with unlike denominators

What you're going to do is try to make your denominators equal (find a least common denominator) You can do this by multiplying both numbers by something so that they are the same. Make sure that you do the same thing to the numerator as you do to the denominator. Typically, you can multiply the numbers by each other to get the least common multiple. Sometimes, one number is a multiple of the other, so you just multiply it by one of the factors to get it. When that happens, it's pretty simple.

For example, you have to add 1/4 and 1/5. The lowest multiple these can both be is 20. I got this by simply multiplying the denominators since they are small numbers. You will multiply 1/4 by 5/5 and get 5/20. Then, 1/5 by 4/4 and get 4/20. 5/20 + 4/20 = 9/20. So 1/4 + 1/5 = 9/20

Also. 1/6 + 3/18. For something like this, you would want to simplify so that 3/18 is 1/6. Then, you'd simply add 1/6 + 1/6 and get 2/6, which could then be simplified to 1/3.

Another thing. 1/2 + 1/4. Here its easy to see that 4 is a multiple of 2. All you need to do is multiply 1/2 by 2/2 and then get 2/4. Now you'll add them since their denominators are now equal. 2/4 + 1/4 = 3/4.

Anyways, that's pretty much it.

You have to find the least common denominator of each number. And remember, whatever you do to the bottom number you must do the same to the top one.