Could you please explain to me why I got this sentence wrong?
Living at home and enjoying your mother’s cooking help you save money.
My teacher said "help" should have been written with an "s".
Why do I need to write an "s" since I was referring to two actions?
The sentence could be read two ways.
One, which you may have intended, is that there are two things that help you save money: 1) living at home and 2) eating your mother's cooking instead of going out to eat or buying your own food.
Another way you could read it is that it is just one thing: "living at home", which has the added benefit of enjoying your mother's cooking. One reason a person might interpret it this way is that "enjoying" isn't really relevant to saving money.
If you wanted to make it clear you meant the first, your could rephrase it to make it clear you meant two different activities. Perhaps something like:
Both living with your parents and eating at home instead of going out to eat help you save money
Actually both are correct. The subject can be taken as a plural conjunction of two items, or as a singular combined whole. I feel like the singular form (what your teacher suggested) is the more typical way to say this, but neither way is wrong!
The form "help you save money" is correct if the subject is plural.
If your sentence has a plural subject, then it has a compound subject made up of two nouns, both gerunds:
The verb to help conjugates as help in the third personal plural. The following elided sentence has the correct form, which matches your original: Living...and...enjoying...help you save money.
On the other hand, if enjoying your mother's cooking is not part of a compound subject, but instead is subordinate to Living at home then the subject of the sentence is the single gerund Living. If that is the case, the idea might have been (better) expressed as Living at home—and enjoying your mother's cooking—helps you save money.
There's also the question of the meaning of the verb to enjoy in enjoying your mother's food. In this context, the gerund might be a synonym for consuming or eating just as well as it might signify relishing or fancying. One might prefer one's mother's food, and yet not eat any of it. Maybe I love cigarettes, but I never smoke.
Since to enjoy one's mother's cooking does not inherently save one any money (which would be the case if you love your mother's cooking yet you live far away from where she lives), a strong argument for the sentence having a compound (plural) subject could be made on the basis of its semantics. Merely living at home would save you money, but if you live at home and love your mother's cooking, you will save even more money. If we're talking about maximum money saving, then we're going with the plural subject.
Forty years ago, a subordinate clause would have been set off by commas, as in: Living at home, and enjoying your mother's cooking, helps you save money. But now we disdain to use such orthography, and so we pay the price of increased ambiguity.
The efficacy of your sentence—as well as the reliability of our assessment of the idea it was intended to convey—may have been diluted to naught, due to the current state of the written tongue's stylistic evolution.
I think that your sentence is not technically wrong, but it definitely sounds wrong when I first hear it.
When I read the phrase "Living at home and enjoying your mother’s cooking," I think that you're talking about one single life choice: the choice to live at home and enjoy your mother's cooking. I then expect you to say that this choice helps you save money. Since it's just one single choice, this phrase feels like it's singular, so it needs to take a singular verb. So, it feels like the sentence ought to be "Living at home and enjoying your mother’s cooking helps you save money."
On the other hand, maybe you want to talk about two separate life choices here: the choice to live at home, and the choice to enjoy your mother's cooking. Maybe you want to say that both of these choices are ways of saving money. In that case, it is technically correct to write "Living at home and enjoying your mother's cooking help you save money." However, as I mentioned, even though this sentence is technically correct, I think it sounds wrong.
On the other hand, this sentence sounds totally fine: "Living at home and enjoying your mother's cooking are ways of saving money." I can't explain why this sentence sounds fine but your original sentence sounds wrong.
I would have to disagree with the singular. "Living at home help you save money" sounds foreign.
The 's' is actually used in third person present tense in the sense of "that helps" and has nothing to do with plural at all.
One of those rules that as a native English speaker I don't even think about - that surprises even me at times.
I would sacrifice a bit of style to obtain increased clarity. If I had written this (in a formal document for people whose grasp of English may not be better than mine) I would have chosen between two versions:
Living at home and enjoying your mother’s cooking both help you save money.
Living at home, and thus enjoying your mother’s cooking, helps you save money.
Or variations upon these. But then I am an engineer and my prose has to be 100% unambiguous. (In fact, I would have written the first with bullet points, but that's just my inner nerd.)
If the intent in the sentence is to talk about two things, each of which could save you money, then the subject would be plural and "help" would be correct. If the intent is that it's a single subject (living at home and enjoying Mother's cooking), "helps" would be correct. "Living at home and enjoying your mother's cooking" is something of an idiom, and would most often suggest a single subject ("helps"). No firm answer can be given here, without considering the surrounding text as context. Either you or your teacher could be correct, depending upon the fine shade of meaning intended.
