Learn Italian: Il triplo del prezzo è troppo caro per me. - Triple the price is too expensive for me.

In Italian, words like il doppio (double) and il triplo (triple) act as nouns meaning "the double" or "the triple". Because they are nouns, you must use the preposition di (of) to connect them to the next noun. Here, di combines with il to make del, literally meaning "the triple of the price".

If the item was a feminine noun, like la tariffa (the rate), would il triplo change its ending?

No, il triplo stays exactly the same. When used as a noun to mean "three times the amount", it is always masculine and singular, regardless of the gender of the noun that follows it. You would just say il triplo della tariffa.

Could I say tre volte instead of il triplo?

Yes! You can say tre volte il prezzo (three times the price) and it means the exact same thing. Notice that if you use tre volte, you just use the normal definite article (il prezzo) without adding the preposition di.

What is the adjective caro (expensive) agreeing with in this sentence?