X does a work in 15 days

X does a work in 15 days. Y does the same work in 30 days. In how many days they together will do the same work?

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 #5949