Some of the 50% solution of acid was removed and this was…

Some of the 50% solution of acid was removed and this was replaced with an equal amount of 10% solution of acid. As a result, a 20% solution of acid was obtained. What fraction 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 #45037