How to add fractions that have different denominators

To solve this problem, we need to find the least common multiple to get at the common denominator. Can you help? We bet you can!
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How to add fractions that have different denominators

Discussion and questions for this video
why does the denominator have to be the same as the other denominator
What does it mean to simplify the problem?
Simplifying a fraction just means putting it into the simplest form. For example, 3/6 can be simplified to just 1/2. They are the same thing, but 1/2 is simplified.
Why does the denominator have to be the same as the other denominator?
Think of it this way:

When you are adding or subtracting two things, they must be the same in order to make it work. If you had 6 basketballs, could you subtract 3 iPhones from them? Of course not!

When working with fractions, the denominator describes the SIZE of the piece, so to do the addition or subtraction, you must make them the same size.

The numerator tells you HOW MANY of each "size" you have, so you only add or subtract the numerator, not the denominator (you aren't changing the "size" of the pieces).

Hope this helps.
If you understand about adding the fractions together, and changing the denominators, see the video on subtracting fractions. (http://www.khanacademy.org/math/arithmetic/fractions/v/subtracting--fractions). There isn't one specifically on subtracting fractions with unlike denominators.
why do you need to multiply the numerator when you multiply the denominator to add or subtract fractions?
Good question. The answer is that if you didn't then you would change the value of the fraction. Like 2/3. If you multiplied both of them by 2, you would have 4/6. Both equal 0.66. If you multiplied the bottom only, then it would be 2/6 which is equal to 0.33. It would change the value.
This should be in the tip/thanks section. (I am not a moderator, but I'm pretty sure this is against the rules as irrelevant)
wow it really helped me ;) ive got a question ..um how do you do this but is there a easy way?
I don't get it at all. He is doing it right but, I don't get the part, I mean all the parts. The only part I get is when you got to times it to find the same number. Anyone can help me pleas do.......