10 prisoners are lined up, each wearing a black or white hat

10 prisoners are lined up, each wearing a black or white hat. Each prisoner can see the hats of everyone in front of them, but not their own or those behind. Starting from the back, each one, in turn, must say only "black" or "white" to guess their own hat color — everyone else can hear, and a plan can be agreed beforehand. Ojas thinks that no matter what plan is made, everyone's chance of being right stays a flat 50%. His teacher says a clever plan can guarantee almost everyone survives. Who is right?