Adverb agreement in Spanish?

Question

I'm doing an exercise that calls for the student to create a question and then answer the question using the phrase ¿Cuántos hay?

So for example, "7 maletas" would be: ¿Cuántas maletas hay? Hay siete maletas.

I looked up cuánto/a in the dictionary and included the definition below. Note that this is a paper dictionary from a college class in the US (Vistas Higher Learning).

Since the dictionary defines the word as an adverb, why does the phrase have to match the gender of the nouns? I thought that was only with adjectives. Is the use of the phrase in this context an adjective then?

¿cuánto/a? adv. how much? ¿Cuánto cuesta? How much does it cost?

Answer 1

According to the definition of the word in the DLE, it is used as a pronoun:

cuánto, ta

3. pron. interrog. m. y f. Qué número o qué cantidad. Usado referido a un sintagma nominal mencionado o sobrentendido, o bien para aludir a uno pospuesto e introducido por la preposición de.

Examples (the parts within brackets are the ones omitted):

Yo me encargo de la bebida, pero no sé cuánta [bebida] comprar.
¿Cuántas [de las novelas] te has leído ya?

So if you say:

¿Cuántas maletas hay?

You need the agreement because cuántas is an adjective that goes with maletas. But if you say:

¿Cuántas hay?

You are omitting maletas because it is understood by context, and then cuántas acts as a pronoun, but still it needs the agreement with the omitted noun.

Indeed, the word cuánto can be used as an adverb, but then it must be used as cuán or cuánto, but not as cuántos, cuánta or cuántas:

¿Cuánto te gusta?
¡Cuán rápidamente caminan las malas nuevas!

You can discern if it is an adverb if you cannot change the masculine, singular form for another one, or if you cannot insert any noun after cuánto (with the exception of "tiempo"):

¿Cuánto [what?] te gusta?
¡Cuánto [tiempo] hace que no nos vemos!

Answer 2

It would be helpful to include a quote from a dictionary, as well as the link to the entry you read.

I think you'll get better results if you look for cuántos rather than cuanto. For example, Collins says:

adj. b. (en plural) how many ¿cuántos días libres tienes al año? how many days off do you have a year?

But Collins has a separate entry for "cuanto." (Still, if you landed there by accident, you could note that none of the sample sentences fit your "maletas" sentence.)

Bottom line, in your question it's used as an adjective.