Learn Portuguese (Portugal): Há cem carros na rua. - There are one hundred cars on the street.

In Portuguese, exactly 100 is cem. We only use cento when we combine it with other numbers to make a bigger number, like cento e um (101) or cento e vinte (120). Since there are exactly 100 cars here, we just use cem.

Since there are one hundred cars, why is the verb há singular? Shouldn't it be plural?

The verb haver (to exist) is special. When we use it to mean 'there is' or 'there are', it always stays in the singular form há. It never changes to a plural form, even when talking about one hundred cars!

Why does the sentence use na for 'on the'?

na is a contraction of the preposition em (in/on/at) and the feminine word for 'the' (a). We use it here because rua (street) is a feminine noun. Also, notice that while English speakers say cars are 'on' the street, Portuguese speakers say they are 'in' the street.

Are cem (one hundred) and sem (without) pronounced the same way?

Yes, they sound exactly the same! You can only tell them apart by context. In this sentence, saying 'There are without cars in the street' would not make sense, so you know it has to be the number one hundred.