Den gamle cykel sælges på loppemarkedet på lørdag.

Because gamle is the correct adjective form before a definite noun.

In Danish, when an adjective comes before a noun that is definite, the adjective usually takes -e:

• en gammel cykel = an old bicycle
• den gamle cykel = the old bicycle

So gammel becomes gamle because the bicycle is definite: the old bicycle.

Den is the definite article used with common-gender nouns when there is an adjective before the noun.

Compare:

• cyklen = the bicycle
• den gamle cykel = the old bicycle

When there is no adjective, Danish often just adds the definite ending to the noun:

• cyklen

When there is an adjective before the noun, Danish usually uses:

• den + adjective + noun

So den gamle cykel is the normal way to say the old bicycle.

Because loppemarked is a neuter noun, and the definite form is made with -et.

So:

• et loppemarked = a flea market
• loppemarkedet = the flea market

This is a very common Danish pattern:

• et hus → huset
• et marked → markedet
• et loppemarked → loppemarkedet

Because Danish usually does not use a separate definite article when the noun stands alone without an adjective.

So:

• loppemarkedet = the flea market

But if you add an adjective, then you normally use det as well:

• det store loppemarked = the big flea market

So in this sentence, på loppemarkedet is correct because there is no adjective before loppemarkedet.

Sælges is the passive form of sælge = to sell.

• sælger = sells / is selling
• sælges = is sold / is being sold

So Den gamle cykel sælges ... means The old bicycle is being sold ... or The old bicycle is sold ..., depending on context.

The -s passive is very common in Danish, especially in notices, ads, and factual statements.

Grammatically, it is present tense, but Danish often uses the present tense to talk about a planned future event.

So Den gamle cykel sælges på lørdag literally uses present tense, but the meaning is future:

• The old bicycle will be sold on Saturday

This is very normal in Danish, just like in English sentences such as:

• We leave tomorrow
• The shop opens on Monday

Because på has several uses in Danish.

Here it means two different things:

• på loppemarkedet = at the flea market
• på lørdag = on Saturday

So the same preposition is used in both places, but with different kinds of meaning:

• location: at the flea market
• time: on Saturday

This is normal in Danish, even if it does not match English word-for-word.

This is standard Danish main-clause word order:

• subject: Den gamle cykel
• verb: sælges
• then the other information: på loppemarkedet på lørdag

So the basic structure is:

Subject + verb + other elements

You can also move another element to the front for emphasis, for example:

• På lørdag sælges den gamle cykel på loppemarkedet.

In that case, Danish still keeps the verb in second position, which is a very important rule in main clauses.

Yes. Sælges and bliver solgt can both express the passive.

• Den gamle cykel sælges på loppemarkedet på lørdag.
• Den gamle cykel bliver solgt på loppemarkedet på lørdag.

Both are possible, but sælges is often shorter and more natural in formal, written, or advertisement-style Danish.

A rough difference is:

• sælges = concise, neutral, common in notices
• bliver solgt = a little more explicit, often more conversational

Usually, yes. In normal conversation, på lørdag most often means this coming Saturday or on Saturday, depending on context.

If the context is already clear, Danish often does not need anything more specific.

So:

• på lørdag = on Saturday / this Saturday

If needed, speakers can add more detail, but in everyday Danish this phrase is completely normal on its own.

Cykel is a common-gender noun in Danish, so it goes with en in the indefinite form and den in the separate definite article form.

• en cykel = a bicycle
• cyklen = the bicycle
• den gamle cykel = the old bicycle

If it were a neuter noun, it would use et and det instead.

So:

• en/den → common gender
• et/det → neuter

Not perfectly. The Danish structure is similar to English, but some parts work differently.

A very literal breakdown is:

• Den gamle cykel = the old bicycle
• sælges = is being sold / is sold
• på loppemarkedet = at the flea market
• på lørdag = on Saturday

But a natural English translation would usually be something like:

• The old bicycle is being sold at the flea market on Saturday.
• The old bicycle will be sold at the flea market on Saturday.

So the sentence is close to English, but not every word maps exactly one-to-one.