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?

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

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).