My thought is that of the 330 who exit, 210 are bounces, which leaves
120 exits that still need to be accounted for. Then taking the 500 total
visitors minus the 210 who left via bounce, there are 290 visits that
still need to be sorted out. Those 290 consist of both folks who arrived
internally (150), and those who arrived directly but didn't bounce (140,
or 350-210). Therefore, the "exit" pool would be the 120 remaining exits
divided by the 290 remaining unaccounted visits, or ~41%.