grammar - "Is" or "are" in: "Where both X and Y [is/are] ..."?

Non-native speaker here. I have the sentence:

• ... where both mean and variance are normalized.

Or should it be:

• ... where both mean and variance is normalized.

I'm not sure which is right here. Thanks for your help.

Answer

"where both mean and variance are normalized"

If you say that two things are normalized, you could say that they are (3rd person plural) normalized.

If you are using "mean and variance" as a single item, then you wouldn't use the word "both," which indicates that they are plural. If you remove the word "both," and add the word "the," then you could feasibly have:

The mean and variance is normalized.

Source:

http://www.quickanddirtytips.com/education/grammar/compound-subjects