A tradesman sold an article at a loss of 20%

A tradesman sold an article at a loss of 20%. If the selling price had been increased by $100, there would have been a gain of 5%. What was the cost price of the article ?

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 #356