depends on the niche, keywords, competition, etc. For instance, if you're in a tough niche (seo, web hosting, loans, etc) you will want as much content as possible, and also to optimize it perfectly. And even then, it won't be enough cause you need backlinks and brand authority and aged domain with aged content and all that crap. But 10 articles of 4k words each is recommended in such a niche.
On the other side, if you're in a narrow niche with very little competition like, for example... I don't know.... dog painting maybe... balloon inflating.... or other nonsense like that, you will want 40 articles of 1k words each, or even better, 80 articles of 500 words each cause the niche is so narrow and competition most likely so weak that you can target 1 keyword with each article, so the more articles you write the more traffic you'll get, hence why you will want to use 40-80 articles of 500-1000 words each.
And there's obviously the in-between niches which will also require different number of words, depending on which keywords you are targeting but more importantly, depending on who your competition on 1st page of google is and what they are doing. If most sites on the 1st page of google in your in-between niche usually have 400-800 words worth of content on their pages you will want to copy them and not overdeliver on content when a few powerful backlinks will help you much more to outrank them.
Anyway, as a general rule, you will want to look at google's first page and see what your competition's content is averaging in terms of words, and try to mimic that. If the sites on the 1st page have between 1200 and 3000 words worth of content (just an example), it's obvious that you can't get away with 500 words article, so in that case a 2000 words article will be recommended to even have a chance of ranking on first 2-3 pages.