How can one connect two separate ideas into a single sentence?
 

In english, one might say "Jill is 25 years old and she works at the supermarket". One could easily break this up into 2 separate sentences, ”ジルさんは二十五さいです。スパにつとめています。 ” But this seems like it would be much more natural to connect them into a single sentence. What is the way to do this? Do we simply connect them with で？

That is probably how I would do it.

Nothing to do with question but the word is スーパー.

I don't see it as 2 separate ideas, it is a person introduction so I see it a same idea. Had you changed the particle it would have been 2 separate idea. Had you written it with を it would have become Jill is 25 years old and she is eating spaghetti.

Anyway, I don't know your level of Japanese, but there are different ways to connect phrases in Japanese. Conjunctions, ーて form, ーたり form, pre-masu form, し...and I am sure there might be more that now I can't think of.

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