with or without "на"
Алекс готовился к экзамену месяц.
Они приехали в наш город на месяц.

These are two sentence from my testbook, I don't understand why "на" wasn't used in the first sentence but was used in the other.

Thanks for your attention

Question

with or without "на"
Алекс готовился к экзамену месяц.
Они приехали в наш город на месяц.

These are two sentence from my testbook, I don't understand why "на" wasn't used in the first sentence but was used in the other.

Thanks for your attention

Answer

Alex has been preparing for a month for the exam.
Them came for a month in our city.

Answer

the same in english
1. Alex spent a month for preparations
2. They came to our city on the weekend ( or for one month)

Answer

How long time made? - Месяц
For how long will be? - На месяц.

Answer

The first sentence says that he spent the month on studying . So we don't use "на". And in the second sentence they came and stayed FOR the month. So we use "на" in this sentence