Learn Dutch: Illegaal vuurwerk is vaak tien keer zo luid als normaal vuurwerk. - Illegal fireworks are often ten times as loud as normal fireworks.

In Dutch, to express that something is a certain number of times more or less than something else, we use the fixed structure: [multiplier] + keer zo + [adjective] + als. In this sentence, the multiplier is tien (ten), followed by keer zo (times as), the adjective luid (loud), and finally als (as).

The lesson mentions using maal zo as well. Could I say tien maal zo luid als here?

Yes, absolutely! Tien maal zo luid als is grammatically correct and means the exact same thing. Keer is slightly more common in everyday spoken Dutch, while maal can sound a tiny bit more formal or written, but they are completely interchangeable in this structure.

Why is there no -e at the end of illegaal and normaal? Shouldn't adjectives in front of a noun usually get an -e?

Usually, yes! However, vuurwerk is a het word. When a het word is used without any article at all (no het and no een)—which often happens with uncountable nouns—the adjective in front of it does not get an -e ending. That is why it remains illegaal vuurwerk instead of illegale vuurwerk.