The chancellor says that there are 76 kids on earth. However when Clarke asked how many wrist bands were removed she was told 24, but 2 kids had already died. Therefore there should only be 74 kids known to still be alive by the station.
Clarke and Finn were playing in the river close to a waterfall. They see blood on the rocks on shore and when they got out of the river to investigate, their clothes were not wet.
About 24 minutes in, when Finn and Clarke go to the waterfall, Finn leans against a tree and you can clearly see his bio-monitor bracelet fall open.