Odpovědělo jen deset procent.

Because Czech word order is much freer than English word order. Starting with the verb is completely normal.

In Odpovědělo jen deset procent, the speaker presents the action first and then gives the subject/result. In English, you usually need Only ten percent answered/responded, but Czech can also say:

Jen deset procent odpovědělo.

That version is also very natural. The difference is mostly about emphasis and information flow, not basic meaning.

In Czech past tense, the 3rd person normally has no separate auxiliary word.

So:

• odpověděl jsem = I answered
• odpověděl jsi = you answered
• odpověděl / odpověděla / odpovědělo = he / she / it answered

In this sentence, odpovědělo is the full 3rd person past form by itself. There is no extra word corresponding to English did or has/have here.

The ending -lo shows neuter singular past tense.

This happens because deset procent behaves like a quantified amount expression, and in standard Czech, subjects of this type usually take neuter singular agreement in the past tense.

So:

• masculine singular: odpověděl
• feminine singular: odpověděla
• neuter singular: odpovědělo

That is why you get:

Odpovědělo jen deset procent.

Even though the real-world meaning is plural, Czech grammar treats this kind of subject as a single quantity.

The dictionary form is procento.

After numerals like pět, šest, deset, dvacet and so on, Czech normally uses the genitive plural form of the noun. For procento, that form is procent.

Compare:

• jedno procento = one percent
• dvě procenta = two percent
• pět procent = five percent
• deset procent = ten percent

So deset procent is exactly the form you should expect.

Yes. The whole phrase deset procent functions as the subject of the sentence.

This is very common in Czech with numbers:

• Pět lidí přišlo. = Five people came.
• Deset studentů odešlo. = Ten students left.
• Deset procent odpovědělo. = Ten percent answered.

In these expressions, the noun after the numeral is often in the genitive, but the whole numeral phrase still acts as the subject.

It can be omitted if the context already makes it clear.

So deset procent by itself can mean ten percent of them / of the respondents / of the people asked, depending on the situation.

If you want to say it explicitly, you can add a noun:

• Odpovědělo jen deset procent respondentů.
• Odpovědělo jen deset procent studentů.
• Odpovědělo jen deset procent lidí.

English uses of, but Czech usually does not use a separate word here. Instead, it uses the genitive case:

• deset procent lidí = ten percent of the people

Jen means only or just.

In this sentence, it limits deset procent, so the meaning is:

only ten percent

So:

Odpovědělo jen deset procent. = Only ten percent responded.

Its position is important because it usually comes right before the word or phrase it focuses on.

Yes. That is a very natural sentence too.

Both of these are correct:

• Odpovědělo jen deset procent.
• Jen deset procent odpovědělo.

The difference is mainly stylistic:

• Odpovědělo jen deset procent puts the action/result first.
• Jen deset procent odpovědělo highlights only ten percent right away.

For a learner, the second version may feel closer to English word order, but both are good Czech.

The dictionary form is odpovědět.

It is perfective, so it refers to a completed act of answering/responding. That fits a sentence reporting a finished result, such as a survey result.

The imperfective partner is odpovídat.

Very roughly:

• odpovědět = to answer, to give an answer, to respond completely
• odpovídat = to be answering, to answer repeatedly/habitually, to correspond

So in this sentence, odpovědělo is the natural choice because it reports a completed outcome: only ten percent responded.