A student gets 60% in one subject, 70% in the other

A student gets 60% in one subject, 70% in the other. To get an overall of 70% how much should get in third subject.

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 #43496