Draw everyone as a square, split it by how common H is, then mark who shows the evidence E in each part. Once you know E happened, only the E strip is left, and the chance of H is simply the share of that strip that has H.
Draw everyone as a square, split it by how common H is, then mark who shows the evidence E in each part. Once you know E happened, only the E strip is left, and the chance of H is simply the share of that strip that has H.