Learn Spanish (Latin America): Hay trescientas cuarenta y dos personas en el hotel. - There are three hundred forty-two people in the hotel.

In Spanish, the numbers for hundreds (from 200 to 900) change their endings to match the gender of the noun they are counting. Because personas is a feminine word, trescientos changes to the feminine form trescientas.

Since personas is feminine, shouldn't dos change to a feminine form too?

No, the number dos (two) stays exactly the same for both masculine and feminine nouns. The only numbers that change to match gender are 1 (which becomes un or una) and the hundreds from 200 (doscientos/doscientas) up to 900.

Why is cuarenta y dos written as three separate words?

For numbers from 31 to 99, Spanish uses a formula: the tens number, plus y (and), plus the ones number. So, 42 is literally 'forty and two' (cuarenta y dos). Earlier you might have seen numbers like 22 (veintidós) written as a single word, but from 31 onwards, they always split into three words.

Wait, I thought hay meant 'there is'. Why is it used for 'there are' here?

The helpful thing about hay is that it means both 'there is' and 'there are'! Unlike English, Spanish uses this exact same word whether you are talking about one single thing or hundreds of people.