Learn Dutch: De zangeres was anderhalve week ziek. - The female singer was sick for one and a half weeks.

In English we say 'one and a half weeks', using the plural. But in Dutch, the word anderhalf (or anderhalve) is always followed by a singular noun. That is why it is anderhalve week.

Why does it say anderhalve here instead of just anderhalf?

Anderhalf gets an -e ending when it comes before a de-word. Since it is de week, we use anderhalve. If it were a het-word, like het jaar, you would use the uninflected form: anderhalf jaar.

The English translation says she was sick 'for' a week and a half. Why is there no Dutch word for 'for' in the sentence?

In Dutch, when you want to express how long something lasted (the duration), you often don't need a preposition at all. You can just state the time period directly, like anderhalve week ziek.

Is zangeres the standard word for 'singer'?

Zangeres specifically means a female singer. The male equivalent, or the general term, is zanger. In Dutch, the -es suffix is commonly added to indicate a female profession.