In a class there are 20 boys and 21 girls

In a class there are 20 boys and 21 girls. In how many ways can a boy and a girl be selected?

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 #20817