How do I add three fractions with three different denominators?

I know how to come up with the common denominator for all three fractions. But how do I change the numerator?

For example: 1/2 + 2/3 + 1/4

Denominator will be 12.

Now what do I do with the top number?

When you change the denominator of a fraction, you must also change

the numerator, so that the actual value of the fraction doesn't change.

You're correct that the lowest common denominator for those is 12.

But I think we have to talk about how you change each fraction to

the common denominator:

To change 1/2 to a denominator of 12, you multiply the old denominator

by 6. So you need to also multiply the numerator by 6. 1/2 = 6/12.

To change 2/3 to a denominator of 12, you multiply the old denominator

by 4. So you need to also multiply the numerator by 4. 2/3 = 8/12.

To change 1/4 to a denominator of 12, you multiply the old denominator

by 3. So you need to also multiply the numerator by 3. 1/4 = 3/12.

Now you have 6/12 + 8/12 + 3/12.

They all have the same denominator, so now you can add the numerators:

(6 + 8 + 3) / 12 = 17/12 = (1 and 5/12).

You have to multiply the denominators by something to get 12 right? well whatever you multiply the denominator by you multiply the numerator by.