A portion of the 80% solution of chemicals was replaced with an…

A portion of the 80% solution of chemicals was replaced with an equal amount of 20% solution of chemicals. As a result, 50% solution of chemicals resulted. What part of the original solution was replaced?

This problem repeats another one in the library (at most with different numbers), so it's left out of browsing.

AQuA-RAT — Algebra Question Answering with Rationales (Ling et al., DeepMind, 2017) · train #24998