Learn Hardcore Chinese: zhè gè wèntí hěn jiǎndān.

个 is a measure word (classifier), and most countable nouns in Chinese need a measure word after a demonstrative like 这 (this) or 那 (that).
So the basic pattern is: 这 + 个 + noun → 这个问题 (this question/problem).

You can sometimes hear 这问题 in spoken, casual Mandarin, but 这个问题 is the standard and safest form, especially in writing or in more careful speech. Different nouns normally use different measure words, but 个 is a very common “default” one.

Does 很 (hěn) here really mean “very”? Is the sentence saying “This question is very simple”?

In this sentence, 很 is often not strongly emphasized as “very”.
In Mandarin, you generally cannot say:

这个问题简单。 ✗ (sounds incomplete or unnatural as a neutral statement)

Instead, you usually add a degree adverb like 很 before an adjective, giving:

这个问题很简单。 ✓

Here, 很 is often just a linking adverb making the sentence natural. Whether it feels like “is simple” or “is very simple” depends on the context and intonation. In everyday speech, with neutral intonation, it usually just means “is simple.”

Why is there no word like “is” in the Chinese sentence? Why not something like 这个问题是很简单?

In Mandarin, adjectives can act like verbs and directly describe the subject, so:

这个问题很简单。 literally: “This question very simple.”

You usually don’t put 是 directly before an adjective in this kind of sentence.
是 is used mostly before nouns (e.g. 他是老师 “He is a teacher”), not before a simple adjective predicate.

So:

这个问题很简单。 ✓
这个问题是很简单。 — only used in special emphasis contexts (e.g., in contrast: “This question indeed is simple, but…”), not as the neutral basic form.

What’s the difference between 这 and 这个? When should I use each?

这 (zhè) means “this”, but when it directly modifies a noun, you normally need a measure word:

这 + 个 + 问题 → 这个问题 (this question)

If you just say 这, it usually stands alone as a pronoun (“this” without saying the noun), for example:

这很简单。 → “This is simple.”

Spoken Mandarin often merges 这 + 个 into one unit 这个 (zhège), and 个 is often in a neutral tone: zhè·ge.

Can I say 这个问题不简单 to mean “This question is not simple / not easy”?

Yes. The normal way to negate an adjective sentence like this is to replace 很 with 不:

这个问题不简单。 → “This question is not simple.”

You usually don’t say 很不简单 unless you want to emphasize something like “quite extraordinary / really not ordinary,” which can have a positive or special connotation depending on context.

What exactly does 问题 (wèntí) mean here? “Question” or “problem”?

问题 has both meanings:

question (something you ask)
- 这个问题怎么回答？ → How do (we) answer this question?
problem / issue
- 这个问题很严重。 → This problem is very serious.

In 这个问题很简单。, it can mean either “This question is simple” (e.g., in a test) or “This problem is simple” (e.g., a math problem or issue), depending on context. The Chinese word does not force you to choose; the situation around it clarifies the meaning.

How are the tones pronounced together in 很简单 (hěn jiǎndān)? Both 很 and 简 are third tone—does that change?

Yes, tone sandhi applies. When you have two third tones in a row, the first one changes to a second tone in actual pronunciation.

So 很简单 is written in pinyin with tones as hěn jiǎndān, but it is pronounced:

hén jiǎndān (2nd tone on 很, then 3rd on 简, 1st on 单)

In everyday speech, 个 in 这个 is usually pronounced with a neutral tone: zhè·ge, so the full sentence sounds like:

zhè·ge wèntí hén jiǎndān

Can I omit 很 and say just 这个问题简单?

For neutral, standard Mandarin, you normally shouldn’t say 这个问题简单 by itself; it sounds incomplete or unusual in most contexts.

However, you might hear something like 问题简单。 in headlines, titles, or very stylistic / literary language, but that’s not the normal pattern you should copy as a learner.
For everyday speech and normal writing, use:

这个问题很简单。

Could I also say 这是一个很简单的问题? Is that the same meaning?

Yes, 这是一个很简单的问题。 is correct and natural. It literally means:

“This is a very simple question/problem.”

The meaning is very close, but the structure is slightly different:

这个问题很简单。 → topic: “this question”; comment: “(it) is simple.”
这是一个很简单的问题。 → “this” = subject; “a very simple question” = predicate noun phrase.

In practice, both are common. 这个问题很简单 is a bit more direct and compact.

How would I say “These questions are very simple” using this pattern?

You can use 这些 (zhèxiē) = “these” and keep the rest similar:

这些问题很简单。
→ “These questions are (very) simple.”

Note that you don’t add an -s to 问题; Chinese usually doesn’t mark plural on nouns.
些 already indicates plurality, so 这些问题 clearly means “these questions.”