Learn Dutch: Het boek is dertig euro. - The book is thirty euros.

Multiples of ten are formed by adding the suffix -tig to the number, which works exactly like the "-ty" ending in English. For "thirty", the base word drie (three) changes slightly to der-, making dertig.

How do I pronounce the -ig at the end of dertig?

The -ig ending in Dutch is pronounced with a short "uh" sound followed by the soft, breathy Dutch "g". It sounds like "uhg". You do not pronounce the 'i' with an "ee" or "ih" sound.

Why does the sentence use euro instead of a plural like euro's?

In Dutch, when you state a specific amount of money, weight, or distance using a number, you keep the measurement word in its singular form. That is why it is dertig euro even though in English we say "thirty euros".

Why is it het boek and not de boek?

In Dutch, every singular noun takes either de or het for the word "the". Boek is a "neuter" noun, which means it always uses het. There isn't a strict rule for this, so you just have to memorize the matching article when you learn a new noun.