Learn Spanish (Latin America): Ese bloque es macizo, pero ¿qué tan rápido se derrite? - That block is solid, but how fast does it melt?

In Latin America, qué tan is the standard way to ask about the degree or extent of something, translating to "how [adjective/adverb]" in English. Here, qué tan rápido directly means "how fast." You will see this pattern all the time, such as in ¿qué tan grande? (how big?) or ¿qué tan lejos? (how far?).

Why is it rápido instead of rápidamente?

While rápidamente is the standard adverb for "quickly" or "fast," in everyday Spanish it is extremely common to use the base adjective rápido as an adverb. Because of this, qué tan rápido sounds perfectly natural and is actually preferred in casual conversation over qué tan rápidamente.

Why is it se derrite instead of just derrite?

The verb derretir means "to melt" when someone or something is actively melting another object (like the sun melting the ice). However, when a subject simply undergoes a change of state on its own, you use the pronominal form derretirse. The se shows that the block is melting itself, rather than melting something else.

Could I use sólido instead of macizo for "solid"?