In a party every person shakes hands with every other person

In a party every person shakes hands with every other person. If there were a total of 105 handshakes in the party then what is the number of persons present in the party ?

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 #4569